Query times vary too much between runs - neo4j

Question

I am trying out neo4j to work on my grade project and I decided to create a database with the datagen provided by LDBC. This datagen came with these queries.
So I decided to run one of those queries and collected it's execution time (I ran them using cypher-shell command). So I collected these times:
553575, 558724, 556443, 556675, 551304, 555385, 552896
Note: I took the first run out because as said in this post the first time seemed to be a spike due to cold-cache.
Everything smooth until here, then I've decided to create some paths with new labels, making the database grow from 1.5GB to 2.4GB. The I decided to run again the queries expecting for them to be slower. For my surprise I saw that the times were substantially smaller.
382331, 380566, 405636, 405953, 407277, 391804, 371134, ....
From this post. I expected them to be like all be around a same time (like the first run) and perhaps bigger, but definitely not smaller.
For the purpose of this question, I am using an AWS machine, especifically the i3.4xlarge instance (16 vCPUs, 122GB RAM and 2x 1.9TB NVMe SSD). The current version I am using of Neo4j is 3.3.5 and I am using cypher-shell as stated above.
Additionally I have no other programs/process running on this machine so I think we can just eliminate that issue (and despite that being the case, it should slow them down, not speed them up).
Thanks in advance, I am just asking to see if someone may shed some light for me on this issue :)
EDIT:
The changes I've made were added some paths between :Message nodes and :Person's. Also some between :Person and :Person, some between :TagClass (other label) and :Person. Additionally, the DB had index on :Tag(name), :Person(name), :TagClass(name) and :Country(name) but for the purpose of executing the query, dropped those.
The original query:
PROFILE
MATCH (tag:Tag {name: 'Arnold_Schwarzenegger'})
MATCH (tag)<-[:HAS_TAG]-(message1:Message)-[:HAS_CREATOR]->(person1:Person)
MATCH (tag)<-[:HAS_TAG]-(message2:Message)-[:HAS_CREATOR]->(person1)
OPTIONAL MATCH (message2)<-[:LIKES]-(person2:Person)
OPTIONAL MATCH (person2)<-[:HAS_CREATOR]-(message3:Message)<-[like:LIKES]-(p3:Person)
RETURN
person1.id,
count(DISTINCT like) AS authorityScore
ORDER BY
authorityScore DESC,
person1.id ASC
LIMIT 100
These are profiles from both runs, due to space only added one plan. I can assure you, they're both the exact same (even on db hits, paths expanded, everything):
1st run:
| Plan | Statement | Version | Planner | Runtime | Time | DbHits | Rows |
| "PROFILE" | "READ_ONLY" | "CYPHER 3.3" | "COST" | "INTERPRETED" | 556443 | 0 | 100 |
2nd:
| Plan | Statement | Version | Planner | Runtime | Time | DbHits | Rows |
| "PROFILE" | "READ_ONLY" | "CYPHER 3.3" | "COST" | "INTERPRETED" | 371134 | 0 | 100 |
Plan:
+----------------------+----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| Operator | Estimated Rows | Rows | DB Hits | Cache H/M | Identifiers | Other |
+----------------------+----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +ProduceResults | 100 | 100 | 0 | 0/0 | anon[349], anon[355], authorityScore, person1.id | 0.0 |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Projection | 100 | 100 | 0 | 0/0 | anon[349], anon[355], authorityScore, person1.id | 0.0; {person1.id : , authorityScore : } |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Top | 100 | 100 | 0 | 0/0 | anon[349], anon[355] | 0.0; 100; anon[355], anon[349] |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +EagerAggregation | 126593 | 1842 | 49948155 | 0/0 | anon[349], anon[355] | 0.0; anon[349] |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Apply | 16025884097 | 49948155 | 0 | 0/0 | person2, anon[219], message3, anon[60], tag, anon[136], p3, message1, anon[167], anon[271], message2, anon[91], person1, like | 0.0 |
| |\ +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Optional | 7317 | 49948155 | 0 | 0/0 | person2, message3, p3, anon[271], like | 0.0 |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 5037 | 49897917 | 49897917 | 0/0 | person2, message3, p3, anon[271], like | 0.0; p3:Person |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Expand(All) | 5037 | 49897917 | 108680609 | 0/0 | person2, message3, p3, anon[271], like | 0.0; (message3)<-[like:LIKES]-(p3) |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 7028 | 58782692 | 58782692 | 0/0 | anon[271], message3, person2 | 0.0; message3:Message |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Expand(All) | 7028 | 58782692 | 58866898 | 0/0 | anon[271], message3, person2 | 0.0; (person2)<-[anon[271]:HAS_CREATOR]-(message3) |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Argument | 7317 | 130898 | 0 | 0/0 | person2 | 0.0 |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +OptionalExpand(All) | 7317 | 130898 | 220191 | 0/0 | person2, anon[219], anon[60], tag, anon[136], message1, anon[167], message2, anon[91], person1 | 0.0; (message2)<-[anon[219]:LIKES]-(person2); person2:Person |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +NodeHashJoin | 7317 | 51779 | 0 | 0/0 | anon[60], tag, anon[136], message1, anon[167], message2, anon[91], person1 | 0.0; tag, person1 |
| |\ +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 341165 | 4241 | 4241 | 0/0 | tag, anon[136], anon[167], message2, person1 | 0.0; person1:Person |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Expand(All) | 341165 | 4241 | 8482 | 0/0 | tag, anon[136], anon[167], message2, person1 | 0.0; (message2)-[anon[167]:HAS_CREATOR]->(person1) |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 341165 | 4241 | 4646 | 0/0 | anon[136], message2, tag | 0.0; message2:Message |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Expand(All) | 372142 | 4646 | 4647 | 0/0 | anon[136], message2, tag | 0.0; (tag)<-[anon[136]:HAS_TAG]-(message2) |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +Filter | 1608 | 1 | 16080 | 0/0 | tag | 0.0; tag.name = { AUTOSTRING0} |
| | | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| | +NodeByLabelScan | 16080 | 16080 | 16081 | 0/0 | tag | 0.0; :Tag |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Filter | 341165 | 4241 | 4241 | 0/0 | anon[60], tag, message1, anon[91], person1 | 0.0; person1:Person |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Expand(All) | 341165 | 4241 | 8482 | 0/0 | anon[60], tag, message1, anon[91], person1 | 0.0; (message1)-[anon[91]:HAS_CREATOR]->(person1) |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Filter | 341165 | 4241 | 4646 | 0/0 | anon[60], message1, tag | 0.0; message1:Message |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Expand(All) | 372142 | 4646 | 4647 | 0/0 | anon[60], message1, tag | 0.0; (tag)<-[anon[60]:HAS_TAG]-(message1) |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +Filter | 1608 | 1 | 16080 | 0/0 | tag | 0.0; tag.name = { AUTOSTRING0} |
| | +----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------+
| +NodeByLabelScan | 16080 | 16080 | 16081 | 0/0 | tag | 0.0; :Tag |
+----------------------+----------------+----------+-----------+-----------+-------------------------------------------------------------------------------------------------------------------------------+------------------------------ --------------------------------+
... Results ...
100 rows available after 371134 ms, consumed after another 0 ms
Note: SO Doesn't allow me to write over 30000 characters so had to reduce the text.

Answer 1

The Cypher planner takes the current characteristics of the DB into account when deciding how to carry out a query. Any changes to a DB can alter the execution plan, which can greatly affect the timing.
The best way to understand timing differences after updating a DB is to do before-and-after comparisons of the query profile. Without knowing what query you are using, and especially without the before-and-after profile information (neither of which were provided), it is difficult to impossible to figure out why the timing changed.
The only guess that can be made, with the little information available, is that the timing had changed because the DB characteristics had changed in ways that caused the planner to alter the execution plan.