Hi Ed,
Aha! Well then. I probably should have guessed that from all the questions you've asked previously (and the fact that this is the Developer forum).
The Formplayer service, when it's down, causes the issues I talked about in my initial post (in Web Apps, App Preview, and a few other places in the App Builder), so I would start there.
If you want to just see if it is up, you can use
commcare-cloud production service formplayer status
and if it's down you can use ... start or if it says it's up but you don't believe it you can try ... restart and see if that brings it back up. If those simple "turn it off and on again" suggestions don't work, the next place to look is the formplayer log files. To see where those are hosted check the output of
commcare-cloud production service formplayer logs
and then SSH into your machine (or if you have multiple, the formplayer machine) where you'll find the logs at the path in the output of that command.
Cheers,
Danny