A service had/has been logging hundreds of errors in the development environment and I reached out to the owning process mgr that the error was occurring and perhaps a good opportunity to log additional data to help troubleshoot the issue if the problem ever made its way to production. He responded saying the error was related to a new feature they weren't going to implement in the backing dev database (TL;DR), and they know it works in production (my spidey sense goes off).
They deployed the changes to production this morning and immediately starting throwing errors (same error I sent)
Mgr messaged me a little while ago "Did you make any changes to the documentation service? We're getting this error .."

50% sure someone misspelled something in a config, but only thing they are logging is 'Unable to parse document'. Nothing that indicates an issue with the service they're using.