Not to embarrass anyone, but I will have to say that you can't measure the passive resistance of a device that is on with a multimeter. It makes a lot of sense that the multimeter is measuring a slowly decreasing resistance when that happens. (Exceptions apply, but this is probably not the case here)
Not sure but I don't think he means measured while operating (as in resistance is declining in real time). More likely rig is off resistance is measured. Rig operates for some times (weeks? months?) user notices hashrate is higher, turns off rig and measures resistance which is now higher.
Correction: resistance is _lower_ lower resistance more voltage..goes from 1.20 ohm to 1.03 or lower - one h-card went as low as 0.99 ohms..These are of course K ohm..1.20K. You get my picture.