PWA - MS Project - User get READ ONLY on specific file - Schedule works fine for others

I have projects on a PWA platform, and I'm encountering an issue with file access and editing in MS Project. One user has created a plan where everything works correctly for him. The plan has been published and checked in, but another user with the same permissions cannot open the file. Instead, the user met with a 'read-only' prompt, preventing him from editing the file. Even after clearing the cache and resetting both PWA and MS Project, everything works as expected with other files, but not this specific schedule.

I have even made a new backup (copy) but still same problem with both files (schedules).

Is there something specifically wrong with this file that's hindering proper editing?