I picked up where the OP left off on this today. I had an Optimus block on my ftw3 3090 and needed to return it to stock today. I have a strix that is a much better overclocker that is replacing it now that I have another Optimus block.
Anyways, I've repadded several 3080s/3090s already and I use calipers to measure factory pads before replacing. Memory is 1.9mm-2.1mm with an average of 2mm. This includes backside, no difference. Always measuring the thickest part of each pad. Vrms are 2-2.3mm with an average of 2.2mm for the thickest parts. I suspect the vrms were the OPs problem.
I use thermalright oddessy 12.6wmk pads, these work great but are stiff and don't like to squish so you cannot use measurements for squishy pads.
For my repad I used 2mm on the front and back mem, 2mm on the vrms, and 1mm on the mosfets. For the VRMs you MUST use a bead of thermal paste or even better if you have thermal putty. You will not get good vrm contact if you don't do this. I used arctic mx4 for this. A 2.5mm pad is too thick. The paste fills the tiniest gap you'll have. This also let's the mosfets make contact with the pad unlike the OP where they have a gap. Core was pasted with TG kryonaut.
I'm still testing but results are great so far. Looping heaven in my open air testbench with the xc3 bios and power sliders maxed(~520w)core temps top out at 70c, mem junction 78c. Hottest vrm reading is 69c. Mining eth tops out mem junction at 92c. I can easily drop this 10c by pointing a fan at the backplate.