Okay I have found a way. Because we can't undervolt via Claymore, I change voltage value in bios, then flash, in order to bypassing Claymore undervolting ^^
Did it work on you? What miner version are you using and what AMD driver?
I've had my overclock/underclock/undervolt settings in BIOS for the past 3 weeks and I'm using aug11 blockchain drivers plus Claymore v9.8 on Win10 Pro and i've never seen it read my voltage offsets.
I then had to fire up Trixx after Claymore is running steady to do my undervolts - worked for me.
Please do share your settings.