When system is loaded, sleep(5) in test_06_dhcp_default_route_for_vrf can be not enough.
In this case

self.assertIn(rf'ip route 0.0.0.0/0 {router} {interface} tag 210 {default_distance}', frrconfig)

fails and lines

self.cli_delete(interface_path + ['address'])
self.cli_delete(interface_path + ['vrf'])
self.cli_commit()

are not run.

As a result, tearDown fails for this and any other test that tries to remove VRF red.