So I'm not sure if I've been having the same issue but in two occasions (yesterday and just now) all avionics and systems froze without me touching a thing. In both cases I was just waiting for the AP to turn into the last waypoint for final approach and then everything freezes and the AP doesn't work anymore. It was a primary route, wasn't even looking at the FMC ahaha!
This was the route: ROTW5B ROTWE DCT NATOR N850 TRA UZ670 BASGO Z424 AKASU DCT VP342 DCT MF506 DCT
Yesterday I had the very same issue at a different route; EDDM - LIMJ, again at the last waypoint.
It seems weird to me since the aircraft was already configured and I hadn't touched a thing, was just waiting for the ILS signal and then to disconnect the AP.
Let me know if there's anything I can do to help identify/reproduce the issue.
P.S: I'm quite new to MSFS having coming from other sims, literally started flying it on sunday, so when this first happened I thought it was some messed up simulated emergency where you just lose all avionics and instead I quickly realised not even the yoke was moving hahahah!