I am seeing something unexpected in the backend apache logs. It may or may not be related to the problem at hand.
I am seeing an HTTP 422 error when scp/login.php is requested. This error is NOT isolated to requests through the load balancer. When I access the backend server directly, the 422 error also shows up in the logs, but osTicket does work fine.
"GET /scp/login.php HTTP/1.1" 422 6480 "-"
Again, the aforementioned apache config for both the frontend and backend servers of my phpBB installation works. The apache logs for the phpBB backend do NOT have any 422 errors, so I am inclined to think that the 422 errors are somehow related specifically to osTicket. Hmph.