I have being suffering from similar symptoms, which started last 2016 summer time. Here in Madrid, Spain, so high temperatures are not so rare in mid August¡¡ but other people were flying and without ESC cuts¡

Trying to know more details, I installed the telemetry (basic one, which give idea of signal quality) module and came out a lot of failings and signals lost. So, conclude the case of motor cuts is because the radio system enters fail safe mode.

After all this time since the begining of the file, had checked and renew the regulator (receiver and servos are feed independently from motor battery), had changed the receiver and so on, as soon as I perform the range test, telemetry give me a lot of fails...

Right now, I am considering to use other branch trasmiter and receiver system.

It is being a nightmare¡¡