I had a similar issue, where a few notebooks popped up as changed in every branch I created (even though they were not touched). So first I manually did the discard changes thing, but that was not a solution as with every new branch they were there again.

So I checked what was 'changed'. And that was in fact nothing so I took those 'changed' notebooks into my PR.

When merging the PR, git detected that nothing was in fact changed, so they were not merged.

On the other hand: in Databricks they would not show up anymore, so the issue seems to be fixed.

The issue popped up after an update so my guess it was indeed a bug.