URL category allowed - blocked with noauth-protocol

Hi All - anyone throw any light on the below please?

Example User is called Fred, he is allowed to go to a gambling site. He could “get to” all of them – but the some sites eg 888casino and betfred don’t actually load – either a blank page or a landing page with a “there might be something wrong with the connection”,

The logs show non https traffic is allowed. But https traffic is not allowed and shows
noauth-protocol$@

Not using ZCC

We have advanced settings on to allow unauth traffic.

Thanks
Sue