I have CTD’s on long flights as well. However I was able to complete a 2,5 hour flight the other day.
I had one CTD flying from KSLC/Salt Lake to KBOS/Boston (1825 mi). It CTD’d at 900 ft just before I was going to disengage the AP. The flight got invalidated (flying on FS Charter) which is very frustrating…
Had a flight from LPMA/Madeira to EDDF/Frankfurt (1533 mi) that CTD’d around Paris just before the descent.
Today from PANC/Anchourage to KORD/Chicago (2467 mi) I had a CTD around 3 hours in flight (mid flight, somewhere over Canada).
I’m pretty sure it is a memory leak of some sort. I never have this on short flights. The only CTD’s other than these are from the menu pages. That is also a bit frustrating, but nothing like a long flight with all the preparation, etc. that gets invalidated… It always puts me off flying for a week or so before trying again.