MOS-LQ will only score calls carrying real voice payloads. If the calls are carrying test traffic (e.g., FPGA generated traffic) then MOS-LQ will be "0".
So check that the SIP User Agents are using "SIP User Agent" profiles that are using "Encoded RTP" (and not "Simulated RTP").
"SIP User Agents" profiles
SIP User Agent device blocks with Encoded RTP and Simulated RTP "SIP User Agent" profiles.