I also got the "reset your password" from Comcast AGAIN (for a second time in 2 weeks) today. I did and once again, I'm back down to 64 TVE channels from about 14X TVE channels.

And here's the specific list of those 64 since that seemed to matter to some before...
So, having already been through this once (and shared above), I tried the SAME process again.
First, I check the Xfinity mobile app on my iPad and- just like before- instead of showing ALL of the channels that are usually there- it was only showing the same very short group as before...
That is what would display when choosing Live TV, ALL channels in the app with NO filters. Normally, there would be well over 150 channels in this app.
So, I did the same thing I did last time: started a chat with xfinity, requested "live help", told them the problem WITH THEIR MOBILE APP (not even trying to mention TVE or the Channels app, so they would see this as THEIR problem and not try to blame Channels or be confused about what TVE is). They put me on hold a couple of times to reset something on their end… then refreshed my own modem and account once. Asked me to log out and log back in. There was a couple rounds of “Now check”… “no still the same”… “Now check”… “no still the same”… “Now check.” Unlike last time, this has to be “escalated.” So I had to exit the chat this time and wait for the escalation people to get back to me (wondering if they would). They did maybe 2 hours later.
Maybe 1 hour later, I checked anew and the full list of channels reappeared in the Xfinity mobile app as normal, I fired up Channels in Safari on my Mac. Did a fresh scan of TVE channels (without waiting 48 hours, etc, setting up a new Comcast user ID, etc)… and all of the missing TVE channels came back…

This makes me believe that once they make you change your password, they have to reset something on their end. Whatever that is doesn't seem to take effect for upwards of a few hours. When they do whatever they are doing and you can see your cable channels in their mobile app guide, TVE can be rescanned in Channels and the missing channels come back. This has worked for me TWICE now, through 2 Comcast-forced “change your password” cycles. This second time, I didn’t even bother to wait any hours at all, try a new user ID, etc).
Same day of losing them after password change, I have them back and they play. While it's no joy working with Comcast customer service, if you really want the TVE channels back ASAP, this may be a good option to try.