As advised on the bugtracker I ran ‘location update’ as root from CLI. Got the database from Tue, 13 Oct 2020 08:21:56 GMT
With this database the location filter works as intended as far as I can see, no GUI or SSH lockout, traffic flows as it should.
This seems to be a dud database in the upgrade and/or install files and insufficient checks on the validity of the database when such a thing can bring down all connectivity 