@m5stack :
So far the "80Mhz" fix is holding up since Oct-21st , running on 2 units.
Program and IDE are the same when running at 240MHz.
When the problem occurs (at 240MHz), both units lock up so bad, that they will not even reboot.
I will try a few more M5StickC running at 240Mhz (with exact same program and programmed from same IDE) and see if they again lock up after a few days.