I placed a video marker. (I am currently not clear on how these markers work compared to daw but that is a different topic)
I tried to move the marker with opt-arrow. It moves forward and backward in the bar according to the grid (I’m going to assume moving the marker changes tempo map… because the marker itself does not seem to change…but that’s a different topic). Then the marker got stuck and would not move forward with the shortcut, it would only move backwards. Dragging it with a mouse was ok, not stuck. Then using opt-arrow shortcut to move it was again ok for several moves. But then it got stuck again, and would not move forward with opt-arrow, but it would move backwards.
Then I changed the marker time and it is not stuck anymore so it is not reproducible.