Do files on shared google drive disappear if one of contributors somehow gets banned/removed from list of people who can access the shared drive? Or maybe if they somehow clear their own drive cause let say they had no space, will the files that they uploaded leave the shared drive?
I suppose that this could answer why files are disappearing. Alternatively google somehow started checking and removing files, but I am nearly sure that if it was that, the whole drive would get marked and insta removed/banned, so thats probably not the reason. So in my opinion you can upload your backups.