500 Internal Server Error fails rendering layout and view content - ruby-on-rails

Question

I'm working on an app that I didn't develop, so there are many things about the architecture that are not clear, yet. My goal is just to get it up and going at this point. I'm helping an organization upgrade a Rails built on 4.2 to run on 6.0.2. I've gone to Railsdiff and other places to learn to change.
After updating and replacing gems, and making other Rails 6 changes, I was able to get the application to boot. The problem that I'm running into is a 500 Internal Server Error and it refers to ActiveRecord. The log shows that the app is arriving at the correct controller/action. It shows where I dumped a couple of records to make sure it was following the app path. It fails when it tries to render the layout and views. Examining the page shows that nothing is rendered. No HTML elements or meta data about the page is visible.
Here is a dump from my development.log file. Everything looks good until the end. If you have experienced this in the past and have suggestions, I would appreciate any suggestions.
Zeitwerk#rails.main: constant CoursesController loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/controllers/courses_controller.rb
Zeitwerk#rails.main: constant CorporationsController loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/controllers/corporations_controller.rb
Processing by CorporationsController#show as HTML
Zeitwerk#rails.main: constant Corporation loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/models/corporation.rb
Corporation Load (1.5ms) SELECT "corporations".* FROM "corporations" WHERE "corporations"."subdomain" = $1 LIMIT $2 [["subdomain", "devdomain"], ["LIMIT", 1]]
Zeitwerk#rails.main: constant DeviseController loaded from file /usr/local/rvm/gems/ruby-2.5.1#academy/gems/devise-4.7.1/app/controllers/devise_controller.rb
Zeitwerk#rails.main: constant ImageUploader loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/uploaders/image_uploader.rb
Zeitwerk#rails.main: constant Announcement loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/models/announcement.rb
Corporation Load (1.7ms) SELECT "corporations".* FROM "corporations" WHERE "corporations"."id" = $1 LIMIT $2 [["id", 1], ["LIMIT", 1]]
Zeitwerk#rails.main: constant PaperTrail::Version loaded from file /usr/local/rvm/gems/ruby-2.5.1#academy/gems/paper_trail-10.3.1/lib/paper_trail/frameworks/active_record/models/paper_trail/version.rb
Zeitwerk#rails.main: constant VideoUploader loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/uploaders/video_uploader.rb
Zeitwerk#rails.main: constant Course loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/models/course.rb
Course Load (2.5ms) SELECT "courses".* FROM "courses" WHERE "courses"."deleted_at" IS NULL AND "courses"."corporation_id" = $1 ORDER BY lower(TITLE) ASC [["corporation_id", 1]]
CourseSchedule Load (1.5ms) SELECT "course_schedules".* FROM "course_schedules" INNER JOIN "courses" ON "courses"."id" = "course_schedules"."course_id" WHERE "course_schedules"."deleted_at" IS NULL AND "courses"."corporation_id" = $1 AND 1=0 [["corporation_id", 1]]
Zeitwerk#rails.main: constant BackgroundUploader loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/uploaders/background_uploader.rb
Zeitwerk#rails.main: constant Instsplash loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/models/instsplash.rb
Instsplash Load (1.2ms) SELECT "instsplashes".* FROM "instsplashes" WHERE "instsplashes"."corporation_id" = $1 AND "instsplashes"."landing" = $2 ORDER BY "instsplashes"."id" ASC LIMIT $3 [["corporation_id", 1], ["landing", true], ["LIMIT", 1]]
Redirected to http://dev-account-on-ec.compute.amazonaws.com:3005/instsplashes/1
Completed 302 Found in 305ms (ActiveRecord: 50.0ms | Allocations: 139299)
Started GET "/instsplashes/1" for location at 2020-03-23 16:27:19 +0000
Zeitwerk#rails.main: constant InstsplashesController loaded from file /home/devuser/webapps/dev/mydevdir/academy/app/controllers/instsplashes_controller.rb
Processing by InstsplashesController#show as HTML
Parameters: {"id"=>"1"}
Corporation Load (1.2ms) SELECT "corporations".* FROM "corporations" WHERE "corporations"."subdomain" = $1 LIMIT $2 [["subdomain", "devdomain"], ["LIMIT", 1]]
Instsplash Load (1.2ms) SELECT "instsplashes".* FROM "instsplashes" WHERE "instsplashes"."id" = $1 LIMIT $2 [["id", 1], ["LIMIT", 1]]
Corporation Load (1.2ms) SELECT "corporations".* FROM "corporations" WHERE "corporations"."id" = $1 LIMIT $2 [["id", 1], ["LIMIT", 1]]
Course Load (1.3ms) SELECT "courses".* FROM "courses" WHERE "courses"."deleted_at" IS NULL AND "courses"."corporation_id" = $1 ORDER BY "courses"."title" ASC LIMIT $2 [["corporation_id", 1], ["LIMIT", 1]]
####COPORATION FOUND IN INSTSPLASHES SHOW {"id"=>1, "approved"=>nil, "request_id"=>nil, "created_at"=>Fri, 20 Mar 2020 14:06:00 UTC +00:00, "updated_at"=>Mon, 23 Mar 2020 16:24:27 UTC +00:00, "name"=>"Dev Account", "stripe_id"=>nil, "facebook"=>nil, "twitter"=>nil, "linkedin"=>nil, "google"=>nil, "support_email"=>nil, "pinterest"=>nil, "you_tube"=>nil, "instagram"=>nil, "tumblr"=>nil, "support_url"=>nil, "phone"=>nil, "badges_on"=>false, "preset_badges_on"=>true, "course_expiration"=>nil, "rev_share"=>100, "no_tax"=>nil, "discussion_on"=>nil, "rating_displayed"=>nil, "feedback_displayed"=>nil, "training_cycle_start"=>nil, "training_cycle_end"=>nil, "website"=>nil, "use_training_cycle"=>nil, "show_blog"=>nil, "allows_sign_up"=>nil, "about"=>nil, "course_approval"=>nil, "enrollment_approval"=>nil, "show_generic_troubleshoots"=>true, "po_requires_approval"=>true, "hide_cart"=>true, "saml_metadata"=>nil, "numanagesettings"=>{}, "saml_privatekey"=>nil, "saml_certificate"=>nil, "payment_gateway"=>nil, "payment_key"=>nil, "payment_secret"=>nil, "service_code"=>nil, "local_ref_pay"=>nil, "allow_instructor_ratings"=>nil, "qr_code"=>nil, "selected_home"=>"corporation", "saml_privatekey_kms_enc"=>nil, "saml_certificate_kms_enc"=>nil, "saml_metadata_kms_enc"=>nil, "course_per_cycle"=>1, "live_classroom_on"=>false, "validate_instructor_sme"=>nil, "show_course_enrollments"=>true, "show_course_modules"=>true, "twilio_service_on"=>false, "twillio_from_number"=>nil, "twillio_account_sid"=>nil, "twillio_auth_token"=>nil, "volunteer_toggle"=>false, "need_organization"=>false}
----INSTSPLASH FOUND IN INSTSPLASHES SHOW {"id"=>1, "corporation_id"=>1, "heading"=>"Page Heading", "name"=>"Page Name", "organizations_on"=>true, "show_courses"=>true, "text_color"=>"#ffffff", "button_color"=>"#543939", "background_color"=>"#ebebeb", "overlay_color"=>"#522b2b", "overlay_opacity"=>"0.45", "landing"=>true, "background_images"=>nil, "heading_size"=>20}
Rendering instsplashes/show.html.erb within layouts/splashpage
Rendered instsplashes/show.html.erb within layouts/splashpage (Duration: 84.5ms | Allocations: 78655)
Completed 500 Internal Server Error in 104ms (ActiveRecord: 4.9ms | Allocations: 83856)

Answer 1

I discovered my problem. It is in the asset pipeline. For some reason it is not finding the assets. I discovered this by commenting out the stylesheet_link_tag's, javascript_link_tag's, and image_tag's. The app started working. Also, there were several UI gems that I had to require in the application.rb file. I'm going to close this out since I know where the problem lies.