Provided that Dave really has replaced these two 1N4007 by the reversed transistor diodes pair, (aka FLUKE protection), which he had promoted in two of his former videos, my prediction that this was useless, and the wrong approach, obviously has come true, as the Ohm range was far off after the overload experiments by Joe.
I'm no real friend of Joes further brutal destructive tests, as they seem to me being exaggerated and not conforming to the IEC et.al. test standards.
But anyhow, the 121GW really has big problems not to detect AC+DC signal overloads.
This has been discovered already when AC+DC current overloads were investigated in another thread.
So this is really a safety issue at high voltages, which should be solved by UEI.
Hopefully this can be done in SW, but I fear that this might be an intrinsic problem of the circuit, or of the chip set, precisely, of the way how AC signals were measured.
Frank