Yes, the polling rate affects it but it will be still too large for such a long period.
Try to disable monitoring of the PresentMon sensor if that will solve the problem.
Not sure what exactly do you mean without seeing a screenshot but if you have a GIGABYTE board then it's most likely the AORUS theme used by HWiNFO. This can easily be disabled in main settings.
Close HWiNFO.
Run "regedit" tool
Navigate to: HKEY_CURRENT_USER\Software\HWiNFO64\Sensors\GpuI2cCache
Delete the entire key.
If that won't help, please attach the HWiNFO Debug File.
If voltage offsets are not shown, then most likely because Windows HVCI (Core isolation/Memory integrity) is blocking access and you will need to disable it to see them.