Nextcloud Mac OS VFS Troubleshooting

Folders either empty or not syncing at all
Remove 
~/Library/Application Support/FileProvider/com.nextcloud etc (this is where the configuration files that tell macOS to mount its providers go - Nextcloud doesn't properly clean these up when you delete the connection).
Uninstall Nextcloud (unless you intend to re-establish some connections; if you don't uninstall it, the folder above will re-appear, albeit harmlessly with just some default entries).
Restart your Mac (must be a restart, not a logout/in, or macOS won't let go enough for you to do the next step).
Go to 
~/Library/CloudStorage in the Finder. Delete the folders that start with 
Nextcloud , I had to do a sudo rm -r -f to be able to do this, but this might not be needed
This will do a full reset on the VFS