Personally, I would much rather suspect the ASUS sensing probes and software. If the voltage was truly nosediving that far..the system would shut down before you could bat an eye. The cpu voltage only needs to flicker under its required operating voltage for it to quit..instantly, and I believe I can assure you if Vcore went to .88 volt, your machine would be on its way to a shut down..
There is only one true way to measure such as what you are doing, and that is by lab type (calibrated) instruments. The devices the motherboard manufacturers but to place on out motherboards are much less than perfect...most being in the 20% tolerance range and above.