Sync failed on Windows app

Sync failed on Windows app

I've just started using the Windows app for Nimbus (v6.45.2) and it won't sync.

The tooltip says:
Authenticating
Downloading meta info...
Last sync: [current time and date] (Sync failed)

I've tried signing in and out, reinstalling.

Works fine on mobile and web browser.

Any help would be greatly appreciated!