@gotwf I have found the culprit, and it has nothing to do with NodeBB, so I'm sorry to have bothered you.
It ended up being our security team turned on web filtering rule on our load balancer that filters out certain URL paths that have admin/manage/etc in the path. The idea being to filter our administration pages and force the use of VPN to get to those paths. It's a fine idea, but I was not informed of that change.

Thank you for your help.