So the 2021 PP has stated doing this again. Upon the multiple crashes/black screens I'm getting (another issue, thanks Adobe), when restarting certain clips appear greyed out and are out of sync with where they should be. Always the same clips everytime this happens. Photo attached. This issue was present in 2020 and then seemed to fix. I've removed all effects from the offending clips, no change.
Getting closer to the point I'm going to have to change software, PP is no longer fit for purpose.