Thanks so much, Peter!
I had considered enabling debugging in the CMS, but assumed that would not help because the error was (presumably) being generated by the player itself. I will try CMS debugging as well as the advanced player debugging as you suggested.
Yes, this was a docker-based installation.
Our player is offline at the moment (totally separate issue) so once it returns to life we’ll try all this and I’ll report back what I found.
Cheers!