Updating here in case it helps anyone else. I don't know why I allowed myself to get bogged down in trying to troubleshoot TVE on channels before following the advice of developers from both Channels and Pi-hole. I didn't understand the link between their advice and my issues until getting TVE back to normal rose to the top of my to-do list again.
Anyway it took less time to fix it than to type this post. I followed the advice from @eric, @maddox and @dschaper above. I created a Pi-hole group named "Bypass" and ensured all the adlists remained on the Default group. I then added the Channels DVR client to Bypass and removed it from Default. Immediately the "no login form" and "adobe auth reg code: no login form found" errors went away. I'm currently scanning all channels again and expect to recover most of the ones I lost. Insert Picard facepalm for not following the directions back in Feb. Thanks again for walking me through the steps!