Applied workaround for issue #2656: Disable new Rails database connection reaping functionality until the Thread-Zombie issue is resolved: https://github.com/rails/rails/issues/33600 .

config/application.rb

@@ -1,6 +1,7 @@
 require_relative 'boot'
 
 require 'rails/all'
+require_relative 'issue_2656_workaround_for_rails_issue_33600'
 
 # DO NOT REMOVE THIS LINE - see issue #2037
 Bundler.setup

config/issue_2656_workaround_for_rails_issue_33600.rb

@@ -0,0 +1,22 @@
+# This temporary workaround for issue #2656.
+# The root cause is an issue in Rails: https://github.com/rails/rails/issues/33600
+# It disables database connnection reaping by setting `reaping_frequency` to 0 for each environment in the config/database.yml file.
+# It restores the DB connection reaping behavior Rails > 5.2 had.
+# It was proposed in a comment on the Rails issue: https://github.com/rails/rails/issues/33600#issuecomment-415395901
+# It was confirmed by @matthewd (a Rails core maintainer) in another comment: https://github.com/rails/rails/issues/33600#issuecomment-415400522
+module Rails
+  class Application
+    class Configuration < ::Rails::Engine::Configuration
+
+      alias database_configuration_original database_configuration
+
+      def database_configuration
+        database_configuration_original&.transform_values do |config|
+          config.merge(
+            'reaping_frequency' => 0
+          )
+        end
+      end
+    end
+  end
+end