Rails Active Storage Preview "Internal 500 error" on Heroku - ruby-on-rails

Question

It was perfectly working yesterday when I had 1 file attached, then I changed to multiple files and previews are not shown anymore.
It seems like I did everything correctly, I even scaffolded another document.
<% #document.files.each do |file| %>
<p><%= link_to "View File", file, target: '_blank' %> |
<%= link_to "Download", file, download: '' %> </p>
<% if file.previewable? %>
<li>
<%= image_tag file.preview(resize_to_limit: [200, 200]) %>
</li>
<% end %>
It is shown like this now
Preview images are shown with 500 error
Maybe it has something to do with Heroku buildpacks, it worked last night or AWS?
Heruku logs:
2018-08-20T15:47:27.158676+00:00 app[web.1]: D, [2018-08-20T15:47:27.158541 #4] DEBUG -- : [1m[36mActiveStorage::Blob Load (5.4ms)[0m [1m[34mSELECT "active_storage_blobs".* FROM "active_storage_blobs" WHERE "active_storage_blobs"."id" = $1 LIMIT $2[0m [["id", 69], ["LIMIT", 1]]
2018-08-20T15:47:27.121163+00:00 heroku[router]: at=info method=GET path="/rails/active_storage/representations/eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaHBSdz09IiwiZXhwIjpudWxsLCJwdXIiOiJibG9iX2lkIn19--dfa8c38d16bcbc65de1a2107a086925141bf585e/eyJfcmFpbHMiOnsibWVzc2FnZSI6IkJBaDdCam9VY21WemFYcGxYM1J2WDJ4cGJXbDBXd2RwQWNocEFjZz0iLCJleHAiOm51bGwsInB1ciI6InZhcmlhdGlvbiJ9fQ==--7c2a4bf0af133050ffc289b97401f795dffdfdbc/EIN%20FunderHunt%20(1).pdf" host=desolate-temple-16025.herokuapp.com request_id=7281973b-884b-455b-83a7-5a85910e790f fwd="71.190.148.218" dyno=web.1 connect=1ms service=2689ms status=500 bytes=1891 protocol=https
2018-08-20T15:47:27.160499+00:00 app[web.1]: I, [2018-08-20T15:47:27.160404 #4] INFO -- : [ActiveJob] [ActiveStorage::AnalyzeJob] [d7e86d99-8801-4bdb-b63a-e1ba4946afad] Performing ActiveStorage::AnalyzeJob (Job ID: d7e86d99-8801-4bdb-b63a-e1ba4946afad) from Async(default) with arguments: #>
2018-08-20T15:47:27.274034+00:00 app[web.1]: I, [2018-08-20T15:47:27.273887 #4] INFO -- : [ActiveJob] [ActiveStorage::AnalyzeJob] [d7e86d99-8801-4bdb-b63a-e1ba4946afad] [36m S3 Storage (111.8ms) [0m[34mDownloaded file from key: wX8vV9RFa3J1bj5Lkynohj14[0m
2018-08-20T15:47:27.415290+00:00 app[web.1]: D, [2018-08-20T15:47:27.414877 #4] DEBUG -- : [ActiveJob] [ActiveStorage::AnalyzeJob] [d7e86d99-8801-4bdb-b63a-e1ba4946afad] [1m[35m (11.8ms)[0m [1m[35mBEGIN[0m
2018-08-20T15:47:27.423905+00:00 app[web.1]: D, [2018-08-20T15:47:27.423324 #4] DEBUG -- : [ActiveJob] [ActiveStorage::AnalyzeJob] [d7e86d99-8801-4bdb-b63a-e1ba4946afad] [1m[36mActiveStorage::Blob Update (3.2ms)[0m [1m[33mUPDATE "active_storage_blobs" SET "metadata" = $1 WHERE "active_storage_blobs"."id" = $2[0m [["metadata", "{\"identified\":true,\"width\":612,\"height\":792,\"analyzed\":true}"], ["id", 69]]
2018-08-20T15:47:27.433985+00:00 app[web.1]: D, [2018-08-20T15:47:27.433860 #4] DEBUG -- : [ActiveJob] [ActiveStorage::AnalyzeJob] [d7e86d99-8801-4bdb-b63a-e1ba4946afad] [1m[35m (3.6ms)[0m [1m[35mCOMMIT[0m
2018-08-20T15:47:27.436119+00:00 app[web.1]: I, [2018-08-20T15:47:27.435928 #4] INFO -- : [ActiveJob] [ActiveStorage::AnalyzeJob] [d7e86d99-8801-4bdb-b63a-e1ba4946afad] Performed ActiveStorage::AnalyzeJob (Job ID: d7e86d99-8801-4bdb-b63a-e1ba4946afad) from Async(default) in 275.23ms

Answer 1

Heroku uses an ephemeral filesystem, meaning that any temporary or uploaded files stored in your application's filesystem will not be available once the dyno stops or restarts.
Everytime you deploy your application, Heroku restarts your dyno. Meaning any uploaded files are destroyed. You should try uploading your files to a service like AWS S3, which ActiveStorage supports.
Here is Heroku's documentation for this. Documentation Link
Here is also a link to an issue on help.heroku.com Why are my file uploads missing/deleted?