It could certainly be a Plex bug but it might be a more general PC problem. Do you do other high-stress tasks on the PC? Maybe try a CPU torture test like Prime95. If you can induce a crash that way at least you know it isn’t Plex.
Win10 64bit has the same problem, when I upgraded to 1.31.0.6654, every night in the task plan to credits detection when the computer will die, can only force a restart of windows, has rolled back 1.30.2.6563, everything back to normal. it seems that 1.31.1.6733 still has this problem, I will wait for the next version in trying to upgrade.