I've had a problem on one of my Windows 10 PCs for a while where the CPU usage spikes when you open the start menu, causing a considerable slowdown which continues for quite a long time afterwards. I'd assumed it was a problem with SearchUI.exe as that seemed to be using a large proportion of the CPU time, but after further investigation today I think the problem is now with dllhost.exe, if I kill that process when it spikes the system returns to normal. Using the sysinternals process monitor shows what dllhost.exe is trying to do at the time, and strangely all it's doing is repeatedly trying to access a non-existent registry key, HKLM\SOFTWARE\Microsoft\EnterpriseDataProtection\Policies

I've looked this up and it seems "Enterprise Data Protection" is something MS added to Windows 10 Pro in the November update, which is when my performance problems first started. Process monitor showed it was failing with "NAME NOT FOUND", so I tried adding the key and also the EDPEnforcementLevel value to tell Windows not to use EDP. Unfortunately this hasn't fixed the problem, dllhost.exe still accesses HKLM\SOFTWARE\Microsoft\EnterpriseDataProtection\Policies continuously, only this time with a "SUCCESS" message.

Does anyone have any idea what's going on here?