I'll bump this with a "me too." It had been working fine with Channels DVR, but then the Xfinity subscription started giving me trouble, so I removed the TV Everywhere source and started to add it back. When I tried that it gave me the same "not in subscription" error. However, when signing into the website the account was able to play the streaming content there without issue.
I even went so far as to delete the service account in Xfinity and make a completely new one, but that has the same issue. As a test, I used a login from a family member's account (who is successfully using it on his own Channels DVR) and I got the same error.
I am running Channels DVR 2021.03.08.2010 with the following specs:
OS
VMware, Inc. VMware Virtual Platform
Linux Ubuntu
20.04 (kernel: 5.4.0-66-generic)
CPU
4 cores / Intel(R) Core(TM) i5-3570 CPU @ 3.40GHz
load averages: 0.15 0.64 0.74
Any suggestions or assistance would be greatly appreciated.