Hello there John,
I'm also experiencing this freeze after 7 hours of running the simulator.
Usually right when I install FSUIPC everything works, but the moment I set up any controls in FSUIPC (even a push-to-talk button on the trigger button on my joystick) it starts to happen.
I will do a test with freshly installed FSUIPC and send you the appropriate logs.
On this link you can also find my test log regarding this issue. I believe you will find it quite robust: https://1drv.ms/x/s!Ajwir6sTKzZQ08gmZpyhaRSh5Gf7zQ?e=OZ3T60
Overall, me and a few other people having this issue managed to isolate the cause to FSUIPC. I don't know how, or why, but when FSUIPC is not selected as an active addon, everything works fine. If it's on, after 7 hours the sim will stop responding to control and keyboard inputs, the plane will go off course and slightly (or signifficantly in the case of QW787) change it's altitude.
Vojta