When copying large files into a synced folder, for a moment Sync will complain that the file is locked. After a while it apparently indexes it, but sometimes it will never sync until I move it out of the folder and back again (on the same drive, so the moving is instant, no locking errors).
The other computer gives a warning, "Cannot download x files" where x is some number. It manages to list the files and everything, but there's no way to actually retrieve them. Restarting either Sync or either computer does nothing. Only removing and re-introducing the file(s) again helps. Just now I updated to the latest version while having the warning, but it's still there.
Both computers are running Windows Server 2016, latest version of Sync (problem has persisted for a long time, don't remember when it started happening).