I’ve seen this happen when I’m using 30FPS footage on a 24FPS timeline, or vice-versa, or if I’m working with a clip that’s been sped up or slowed down. Are the clips you’re having trouble with the same frame rate as the project? Are they sped-up or slowed-down? Trying to help zero in on the cause so the devs have more to go on to troubleshoot.
I am editing in a 24fps project and the drone footage I am including was shot at that frame rate as well as some at 30fps. I am also using some stock shots from Storyblocks and they are in various resolutions from 1080p to 4K as well as frame rates from 25fps to 30fps. There are even a couple listed as 31.58 fps.
Now that I go back into the project time-line to see which clips are showing that glitch, nothing. It appears they are all A-okay now. Very strange because this was popping up all through the latter part of the edit and now they appear to have self-corrected. Anyway, would be worth taking a look at what may be causing this intermittently. It's a minor thing but nice to not have to deal with it.