Google Drive appears to have lost some of it's users files

So from the rest of the comments it seems to be the desktop client. That thing is a bit of a dog of a program to be honest. I have a couple of offsite backups. I think I will keep them as archival moving forward and get even more backup drives. Anyone know a good tool I can use on a mac to compare my old backups with my current drive contents to check for missing folders / files? I use freefilesync at the moment to backup my plex library, I suppose that would be a good place to start?