I wasn't exactly sure where to post this as it does cover mobile, CPU undervolting, Windows 10 update and XTU update.
Previously I was running on a -69 mV undervolt for the core and cache of my laptop's i7-4500U on Windows 10 1809 version, using XTU 4.4.
I updated to Windows 10's 1903 version with the "remove apps and settings but keep files" as the straight upgrade wouldn't work for some reason. Then XTU 4.4 refused to install, something about a specific file not executing, so I installed the latest XTU version.
Right now I am stuck at -59 mV undervolt for the CPU, and still finding a stable undervolt for the cache (already below -60 mV). I also noticed that according to XTU, thermal throttling kicks in at 80C and more frequently compared to previous Windows 10 version. Maybe its the driver interactions, as I did notice three devices/components in "Device Manager" are lableled as unknown with missing drivers compared to the previous Windows version that only had one unknown device. It is a 5 year old laptop, and I recall that years ago, the OEM stated that Windows 10 version 1607 were not supported for my laptop model (aka "plz buy our newer laptop instead" marketing).
I've also tried Throttlestop, but it seems the loss of undervolt stability also carried over. I could use Throttlestop to disable thermal throttling, but that means disabling Core Isolation's memory protection as the developer said they lacked the resources to make the program compliant with Windows 10's security requirements.