Marker Formatting: Use simple names in the comment field (e.g., start) and ensure all time values are whole frame numbers, and not set as something like 1.5.
If you adjust your composition frame rate after setting your markers, this can cause the markers to sit in between two frames instead of on a whole frame. Make sure to adjust the marker manually in the composition to snap to the whole frame number.\
Timing: Aim for video clips of at least 5 seconds, so do not make the duration from video_start to end marker too long, to support short replay clips.