I've been having this same issue since I moved my Google Drive folder to a pooled drive.
Every time I restart my computer (or the application), Backup and Sync behaves as if all of the files are different and "uploads" them. Fortunately, it seems that Google Drive is smart enough to detect that the files haven't actually changed as I do not see any activity on the web UI. This is annoying though as the process takes quite a while and there is conflicts for files that I actually changed.
As a result, I decided to move my Google Drive folder to a standalone drive (along with my Plex