Steps to reproduce:
Compatibility mode helps. In Safari works fine. I don't know how to reproduce it but if I click "reject all" I cannot log into my account, so every time when I open YouTube I see this cookie banner. By the way, with other Google services everything is ok, I have problem only with YouTube.
Orion, OS version; hardware type:
Version 0.99.122-beta (WebKit 615.1.11.7)
MBP 14
Images/Video