I wonder if you should test the ESC which reports the temperature and shuts down the motor correctly on ground test on the plane that you have issue with originally. It could be that the ESC in that plane may act up in high temperature.

I have experienced similar issue before here in Texas and concluded that the pack just can not hold the charge any more as reported by the ESC (min voltage during the flight is 31 V). The error code from Jeti Spin 99 is C = Y.