Gitlab looses threads from diff view after pushing new changes

Summary

Threads not shown in new versions of a diff.

Previously threads on lines changed were kept and one could work in a diff without the need of switching to overview. Files on which comments were made no longer display them and only ability to see them is either change the diff version or go to overview which makes reviews a very painful process.

Steps to reproduce

1. Create merge request
2. add comment on line in a file
3. Change the line, push changes (doesn't matter if rebase&force or new commit)
4. overview shows thread
5. diff no longer shows previous threads, not even an avatar or info that there were actual threads in the past

Example Project

melkorm/php-testing!2 (diffs)

What is the current bug behavior?

Threads disappear after pushing new changes.

What is the expected correct behavior?

Threads are visible after pushing new changes.

Relevant logs and/or screenshots

Will add if needed.

Results of GitLab environment info

Could reproduce this at gitlab.com and on prem instance