Thanks for the assistance!
I switched to encoding HTML entities only and it’s fixed the formatting issues on the Indexers Available page (when I’m able to access it). However, the 503 and 504 messages remain.
I set up debugging but the debug.log file is empty. The general error logs only show memory issues from 2019, so I don’t think they’re related.
I use version 2.0.5 of Email Encoder, version 2.3.03 of UPME, and version 5.3.2 of WordPress. Let me know if you need more info.
Thanks