I've been having this issue for several months now: I usually keep my timeline rendered as I edit. The problem is, after rending, there are usually several clips throughout the entire sequence that won't playback. The program monitor will stay frozen on the last frame of the previous clip. If I pause the timeline on the suspect clip, it will eventually report a "Error retrieving frame xx" and a "Frame substitution recursion" error.
Every time I render an entire 2-3 minute timeline, there are usually 2-5 clips that will do this. The only fix is to delete the render files for the clips and re-render them. I've tried switching between ProRes and .h264 render formats. I edit off of an external SSD (Samsung T7) but the scratch disks are on the internal hard drive. I have a 2019 5k iMac and keep Adobe updated through Creative Cloud.