Hello Dave,
I've seen this now on a couple flights so I think there is something to this issue other than my old FSUIPC7 I was previously running (and I have since upgraded).
In my last flight I was flying from KSLC to KLAX just following a simple flight plan with no SIDs / STARs. Once I got close to KLAX I was handed off to Approach. Approach assigned me an approach to the ILS 24L runway "at pilots discretion" and said to report back to Tower when established on final.
Once I was established I waited for the virtual co-pilot to change frequencies but that never happened (I was on co-pilot mode 2). I just left PF3 alone for a little longer but eventually I changed to the tower frequency myself. The hot-key window then changed to the Tower options (so PF3 recognized the frequency change), and then I hit Hotkey #1 to request a landing but nothing happened, and from that point on I lost all communication with ATC and just had to land without clearance.
Once I finished the flight I tried to disconnect PF3 from the simulator but it got stuck saying it was waiting for disconnect to complete... (see attached screenshot). I eventually had to close it using the System close button on the title bar (which did close PF3 finally).
Anyway, whenever you have a sec maybe you can see a pattern in my logs (which I've also attached).
Thanks!