Have run into this issue multiple times and have had more than a few 1+ hour long phone calls with Comcast while the rep struggles to solve it and then it only happens again a few months later.
Posting here in case others have found a permanent fix. The problem:1. Hbo Go kicks us out
2. Click "Sign In"3. Prompted with activation code
4. Go to hbogo.com/activate and enter code correctly
5. Instead of activating, it just goes to the generic Xfinity account home page
Anyone else have this issue? Working on escalating now to Tier 3 support at Comcast, as it's pretty infuriating to pay for HBO Go and have this happen constantly.