Problems with .mov files after Big Sur upgrade

I just started working on a movie I haven't opened for a week or two. All of the .mov videos are missing from project assets. The cursor stops at the first video during play - but you can hear the sound associated with the video. The app asks where the videos are, I navigate to the file and click on it; it asks for the same .mov file again. 

I tried to delete the movie files and try again. There are errors on every single file. These are the same exact files, with no editing, since the last time I worked on this movie. The videos play just fine outside of the app. 

I opened a new movie and tried to import the files in question. I got errors on every .mov file. 

I did upgrade to Big Sur since the last time I worked on the video. That is literally the only thing that has changed. 

Help!