Hi,
I have the exact same problem : “USP is not accessible” error in the console panel and nothing appear when enabling v2.0 (v1.x still works though).
I think I’ve tested all the possible configurations between the WordPress and Quantcast admin panels, and double check that CCPA is disabled WordPress-side (Automatically add footer CCPA message > Disable) and Quantcast-side (only GDPR is checked under REGULATION).
You can see the error in action on https://blog.op1c.com/.
BR,
Simon