I have the same issue, no matter which plane I am flying, initially the conversations goes well, but after some time it is not working, I have to keep the ATC window opened and to see when ATC is talking, practically the message appears but nothing on speakers. What I am quite sure is that has started after 40th Anniversary update. Before was ok. Initially I suspected strength of the internet, but playing offline has the same problem. I have check in settings, I was thinking that some changings is needed but I nothing found to change in favor. If someone managed to fix this pls let us know, or maybe would be fix it with the next update.