Facepalm: It appears that Microsoft has found itself in a position where it will have to issue a fix for a fix. A patch the company pushed out on September 10 is reportedly breaking the Search option in the Start menu and Taskbar.
The KB4515384 patch was released to address an issue related to Cortana and the search box. It seems that following an update, the SearchUI.exe process was causing spikes in CPU usage.
While the patch does seem to have fixed the CPU spiking, it’s brought new issues for certain users. Some Redditors write that performing searches via the Start menu brings up a blank window, while others say a Critical Error warning is informing them that 'Your Start menu isn't working. We'll try to fix it the next time you sign in.'
Microsoft is reportedly aware of the problem and is now working on yet another fix. Until then, users who haven’t installed the patch might have to decide which is the least annoying issue: CPU spikes from using Cortana and search or having no working search option at all.
As noted by TechRepublic, other unfixed problems in version 1903 of Windows 10, in addition to the CPU spiking, include some PCs failing to install updates, and the discrete Nvidia GPU disappearing from Device Manager in the Surface Book 2.
Back in July, Microsoft started to force-update Windows 10 machines from version 1803 to 1903.