Attempt to put everything in the transaction block

app/services/merge_requests/post_merge_service.rb

@@ -8,7 +8,7 @@ module MergeRequests
   #
   class PostMergeService < MergeRequests::BaseService
     def execute(merge_request)
-      return if merge_request.merged? # nothing to do, this worker has already run at least once
+      # return if merge_request.merged? # nothing to do, this worker has already run at least once
 
       # These operations need to happen transactionally
       ActiveRecord::Base.transaction do
@@ -20,7 +20,6 @@ module MergeRequests
         # Better to have duplicate notifications than no notifications.
         todo_service.merge_merge_request(merge_request, current_user)
         notification_service.merge_mr(merge_request, current_user)
-      end
 
         # These operations are idempotent so can be safely run multiple times
         close_issues(merge_request)
@@ -28,6 +27,7 @@ module MergeRequests
         merge_request.update_project_counter_caches
         delete_non_latest_diffs(merge_request)
         cleanup_environments(merge_request)
+      end
 
       # Anything after this point will be executed at-most-once. Less important activity only
       # TODO: make all the work in here a separate sidekiq job so it can go in the transaction