I've noticed this too. Turning the audio selectfor for COM1, COM2, or COM3 on allows the incoming comms (ATC > cockpit) to be heard from the respective channel, but no outgoing comms (cockpit > ATC) are heard anymore.
Had this yesterday myself - what seemed to have triggered the freeze in my case was requesting ATIS from the ACARS menu. Definitely not persistent as I tried this action again in a later flight without issue.