Update: Solved!
I managed to fix the issue. It turns out I just needed to change the Matching text ID merging setting to "Merge If Types Match" and then gather the text again.
This properly merged the Prefab's ID across all scenes into a…
Hello Chris,
Sorry for taking up your time. I reverted the project to an earlier version and tried updating it again - the problem completely disappeared without a trace.
Thank you very much for your reply !
After struggling all night to find the cause, I finally discovered that when creating a Canvas, Unity also adds an Event System by default. Simply deleting this resolved my problem.