Thanks for the reply. Reading your reply and finding all my setup notes from back when I had first installed ADBTuner got me on track. I did a "cd" command in Terminal (macOS) to go into the directory holding my docker-compose.yml file, and ran the "docker-compose up -d" command. All is working now (to be determined if the problem rears its head again). I did run the logs command, and the log entries were all from when I got it back up and running.
I do have the latest version, I believe. Even though I created this outside of OliveTin and Portainer, the stack does show up in Portainer with Control "Limited", and Watchtower seems to keep it up to date.
The odd thing was that this popped up now, after running with zero issues for months. I'm not sure what the change was. Around the same time, I also noticed a change in Streaming Library Manager, where it dropped Apple TV+ from my streaming services and I lost all those shows until adding it back (I don't think I would have had any reason to have done that, but it's possible a misclick on my part happened somewhere).
Thanks for the reply.