I have also just experienced the marker off by on frame issue.
I believe it is related to the newly introduced time formats, as it only happens in non integer project framerates (ie: I can reproduce it in 29.97 but not 24 or 30)
- for 1080p29.97 i can see the issue starting exactly at the 34;00 second mark and ends at 59;21
- if changing the time format to “frames” it doesn’t happen anymore
here’s a demo with only a color clip in a new project