I can't seem to figure out what happened but Youtube stopped being pulled into our unsanctioned cloud apps on 11/15. I tried watching a video and usually it appears in the alert right away but the only alerts showing up are from 11/15. Nothing changed on our end that we know of.
It would be helpful to see the Real-time policy rule you have that you are expecting to match to block YouTube video streaming.
If you are relying on a policy based on the "CCI App Tag" = "Unsanctioned" then might be worth double checking that YouTube in your CCI page is still showing as "Unsanctioned" (as per screenshot below)
Further, if there have been any new Steering Configurations, the default is to bypass Video Streaming sites; so make sure you are still steering YouTube to Netskope:
Finally, check SSL decryption to be sure that you are not disabling SSL for Audio/Video streaming
(Policies --> SSL Decryption) or to be sure, go to Youtube.com and look at the SSL Padlock in the Browser near URL bar. Do you see the Netskope SSL certificate as the root CA?