Do what you wish.
There is a problem shared in this thread. I've posted a potential solution that did work for me. It could be coincidence but I suspect the action I took did solve this problem (for me) too. I offered the idea not to praise or pan Comcast customer service but to try to contribute a potential solution that does not involve waiting 48 hours or setting up a new username, etc.
Yea, i understand that, and thanks for your input and statement of what worked for you.
But like i said, may or may not be the same exact issue, or root cause of issue.
Especially i question is since u say you also did not see the channels on the Xfinity Stream site, and the number of avaible channels changed in Channels DVR server, those ARE key unique difference in symptoms here.
The devs posted in the main thread that is appears to be "rate limit issue" of trying to much to fast to authorize a device (TVE) and that caused the failure to authenticate when trying to re-add it. only waiting to after the limit time period has worked so far.
Of course, calling in and having them reset it or mess with your account, may result in that limit being reset and resulting in the ability re-add Channels DVR...that is kinda a assumed given solution tatic.
TVE is a Fickle Mistress.
For me I got it to work after forced changing of my secondary Xfinity account password by logging into nbc/live in a PC web browser and then adding Xfinity TVE in Channels. Before I did the separate nbc/live login I kept getting a screenshot when trying to add the Channels TVE account that said need to change your passowrd. Maybe some caching on Channels end or Xfinity's end.
Plenty of posts showing there are issues.
For me, once I get the Xfinity TVE channels scanned and added, they're very stable.
If I ever loose one or more channels I will update to the latest pre-release DVR and attempt to rescan the individual channels instead of rescan all or delete and re-add.
I just created a Viewer account that has no access and cannot change the password... and it appears to be working ... will no longer delete and re-add XFINITY TVE... because I see that if it fails it will eventually come back.
I donât know the count offhand but a lot of the TVE channels are âfreebiesâ that donât even use your provider credentials. I wouldnât be surprised if there are sixty of these, so having 60 channels may very well mean your provider authentication isnât working for any.
True, at last count 62 of them starting with 6700
6700 AS-RICKANDMORTY
6701 AS-THEERICANDRE
6702 AS-THEVENTUREBROS
6703 AS-OFFTHEAIR
6704 AS-MRPICKLES
6705 AS-ROBOTCHICKEN
6706 AS-BLACKJESUS
6707 AS-AQUATEENHUNGER
6708 AS-SAMURAIJACK
6709 AS-INFOMERCIALS
6750 BUZZR
6751 COMET
6752 CHARGE
6753 CONTV
6754 REVN
6755 TBD
6756 DOVE
6757 NASA
6758 NBCNEWS
6759 NEWSNET
6760 CHEDDAR
6761 CHEDDARBIZ
6762 ETLIVE
6763 FRANCE24
6764 NEWSMAX
6765 CBSSPORTSHQ
6766 CBSNEWS
6767 ABCNEWS
6768 BLOOMBERG
6769 NHKWORLD
6770 COURTTV
6771 DW
6772 CAS
6773 CMCUSA
6774 CMC
6776 WEATHERNATION
6777 PBSKIDS
6778 FSTV
6779 RT-AMERICA
6780 ALJAZEERA
6781 DABL
6782 STADIUM
6783 AMGTV
6784 LX
6900 EWTN
6950 EVINE
6951 HSN
6952 HSN2
6953 QVC
6954 QVC2
6955 QVC3
6970 NY-CBSNEWS
6972 LA-CBSNEWS
6973 LA-KTLA
6974 BOS-CBSNEWS
6975 SF-CBSNEWS
6976 MINN-CBSNEWS
6977 DEN-CBSNEWS
6978 PIT-CBSNEWS
6979 PHI-CBSNEWS
6980 CHI-CBSNEWS
6981 DAL-CBSNEWS
I didn't take note of the 60 or so channels I had while the rest of the TVE channels were missing but that does look like the list. I do recall my 60 starting with that first group in that list. And the TVE channels I actually tend to watch sometimes are mostly not in that list of 60.
and comcast is broken again 
My Xfinity Channels are still working fine...at this moment.
Good to have someone to share the misery with
its been almost a week since an update as well 2020.08.12.1854, maybe the "beta" updates broke it?
This should be fixed in v2020.08.19.2205