Am scratching my head over this one. I'm working on a little scamp of a silly idea, but there is loads of glitching taking place. It didn't until I rendered everything out. Then the glitches started appearing - artifacts in the shape of masks on different layers. One weird thing happened too - there was a freeze frame from a clip that was further along the timeline way away from the playhead, but it was showing up on the canvas the whole time, even when I made every layer invisible.
Here is a link to a little export I made of the clip, and then a screen rec of me going through the AEP.