Worth checking if the YouTube Virtual IP is still the same. You can open command prompt or terminal on your laptop to run ping restrict.youtube.com
and put the ip in the box, see below screenshot. As it only happened after the upgrade, so it may not be the virtual ip gets updated but worth checking.
Also you can try to recreate the test URL filtering profile with the same configuration, then apply to a test SSID to ensure it is not due to the upgrade process for not carrying over all the old config to the new config.
If no luck after all, time to open a ticket with the tech support team. Hope it helps.