In case anyone else encounter this issue - I believe this was actually a DNS issue, in that I was working on a dev site that was using my local configuration to point to the domain until I was ready to fully migrate the site. Once I switched the DNS over, I encountered the error described here:
Which I then resolved by downloading the recommended version of Saxonhe (9.7.0.10J) and placing it in my /usr/share/java folder, and pointing to that version of saxonhe.jar in my wp-config file.
Good luck everyone! 