Interesting - I have almost the same setup ... running GSX, Fenix A320 and MobiFlight.
When I've been flying online with VATSIM using vPilot, and within the last 5 or 10 min of the flight (approaching the circuit area) my MSFS CTD. Unless coincidentally, it often happens when I go to adjust the HDG knob.
The reason I query FSUIPC as a possible culprit, is because when I go to Windows Event Logs (Windows+X keys / Event Viewer), and I look for the MSFS CTD, it says the cause of the CTD was FSUIPC (in each instance of this happening).
CTD Data excerpt from Windows logs:
Faulting application name: FSUIPC7.exe, version: 7.4.1.7, time stamp: 0x66d82cd2
Faulting module name: ntdll.dll, version: 10.0.22621.4111, time stamp: 0x518e67bb
Exception code: 0xc0000005
Fault offset: 0x0000000000033faa
Faulting process id: 0x0x120AC
Faulting application start time: 0x0x1DB0D9DC187A81D
Faulting application path: C:\FSUIPC7\FSUIPC7.exe
Faulting module path: C:\Windows\SYSTEM32\ntdll.dll
Report Id: 931a5ee7-576a-49ed-b33c-a98b6e5734ea
Faulting package full name:
Faulting package-relative application ID:
Are you able to please offer any assistance, thanks?