New Microsoft/Intel microcode update KB4100347 breaks Haswell-E and Broadwell-E overclocks

Multiple users on the X99 platform have confirmed and are reporting that their tweaks and overclocks are no longer working after they got Microsoft update KB4100347 installed. This is an Intel Meltdown related vulnerability microcode update. 

Basically what some (but not everybody) end-users are reporting is that once the update (Intel CPU Microcode update) has installed, their tweaks and overclocks are bust and cannot be re-enabled as the PS sticks to reference clocks. This has been reported with X99 setups from multiple manufacturers.

Some examples of users experiencing issues:

• before the update the proc was running 4.2Ghz on all cores but after this update, the Cpu runs Default 3.7 all cores with 1xCore @ 4Ghz.
• I have a 6850k that had an OC of 4.4 now I'm being clocked down to 3.8 it is really pissing me off, at least now I know it's not just me though.

From the looks of things, this could be an incompatibility issue with the BIOS microcode and the UEFI/OS microcode. And that would mean a BIOS update is a mandatory requirement (if available).

You can uninstall the update and it will fix the problem, It is only an Intel update anyway and my 6850k isn't on the list. To uninstall go to Windows Settings-> Update & Security -> View update history -> Uninstall updates, then right click on the update with (KB4100347) and click uninstall.

Users report with the KB update removed, their overclocks come back to life.