In my case, I have given up trying to help AirNav RadarBox with my station's MLAT data. I had contacted support and, after some back and forth as I re-installed the MLAT package and the problem remained, I was then asked whether I am also providing MLAT services to any other organizations. I replied that, yes, I am providing MLAT for FlightAware and ADSBExchange. After I sent that reply, AirNav RadarBox stopped communicating with me.
Perhaps RadarBox has gone the route of FlightRadar24, who have explicitly requested that feeders providing MLAT to other orgs disable MLAT to FR24 (which I did)? At this point, I've been left to guess that RB detects other MLAT feeds and then intentionally disables any synching. That may protect RadarBox from some bad data, but the methodology (no explanation, poor communication) shows low respect for us feeders.