It sound strange that if you access /fop2/admin it will cause the heartbeat/monitor service on FreePBX to time out. The fop2 manager makes a socket connection to the fop2 server, if that connection is blocked, then the php script will block, but not the whole web server. If that is the case, your web server is badly configured as one thread/request should not block others. Are you sure the problem is related with FOP2?