"as they scroll through the thumbnails the images won't display in the full size view and then they get an error message when switching modules"
Two solutions that fix most occurrences of this issue:
- On Mac, grant LR Full Disk Access:
LR can act very screwy without it, and Adobe hasn't managed to modify the LR installer to avoid the need to do this.
- Try resetting LR's preferences:
LR sometimes soils its preferences file, and resetting it can fix all sorts of wonky behavior. That article explains how to restore the old preferences if resetting doesn't help.
- If neither of those help, then see this Adobe help article: