Does this perhaps happen when you update the driver while HWiNFO is running? Try to close it before updating if that will happen too.
When I closed HWiNFO then did a clean install of the latest driver the GPU Temperature Decimal value did NOT reset to 1.
I did the following:
1) Closed HWiNFO from the system tray
2) Opened GeForce Experience and reinstalled the latest driver (clean install)
3) After it completed I reopened HWiNFO64 and the GPU Temp decimal place value was still at zero.
Additional notes that may be relevant:
1) I did not close RTSS for this test -- it remained open
2) When I saw the issue happen, I was updating from an older driver to a newer driver and driver installation required a reboot -- I have HWiNFO64 and RTSS set to open on system startup (where HWiNFO I must launch first or sometimes it fails to catch RTSS for the custom overlay -- probably not relevant for this issue though).
So, for the test I did just now where it did NOT get reset to 1 decimal place (gpu temp under custom tab) I was just clean installing the same new driver (as there wasn't another new one for me to move to). Thanks for your hard work, I love HWiNFO, it's awesome. Best overlay combo around with RTSS imo.