I too have this same Issue with my SDS200 Scanner & receiving of my Statewide P25 Trunked Radio System as to where I have to have my Squelch turned all the way down to ZERO or even less. Otherwise, my SDS200 Scanner will not stop on or land on any of the active TGID's when there is something going on. I will instead, clearly notice & see it passing right by active P25 Trunked Conversations that are happening & being received on it if I set the Squelch to 2 or above regardless of what Antenna I am using, RF Amplifier, etc.
I'm not sure if it will ever be fixed, addressed or even looked into by Uniden for a possible fix being that we keep going longer & longer without any promise or signs of new future or upcoming SDS Firmware Updates?