Cannot edit the translation because someone edited the file the same time

I am working on translation in ArcMenu project since 2019.
Since some months every time I want to edit a po file I see this error message: Someone edited the file the same time you did. Please check out the file and make sure your changes will not unintentionally remove theirs.

So I have to delete my fork of ArcMenu and after that I have to fork it back again. Now I can edit the file as usual and open a PR.

Can you tell me what´s the problem?

Kind regards.