An emergency patch released by Microsoft to fix Cortana's high CPU usage is said to have broken Start Menu and Search functionality on Windows 10, users have reported.
There's also reports that it's causing issues with Action Center and external USB devices, such as keyboards.
Windows 10's KB4515384 patch was issued on Tuesday following complaints of massive spikes in Cortana CPU activity after installing the most recent Window's update.
Alongside the Cortana fix, Microsoft also said it had found an issue with SearchUI.exe causing similar CPU spikes for a small number of users, both of which have now been marked as resolved on Microsoft's support page.
However, users are now reporting the patch has resulted in even more broken elements, including problems with the Cortana search bar, and USB devices.
"Typical Microsoft, fixes the CPU usage by completely breaking search so it can't even be used..." one user wrote on a Windows 10 hub on Reddit.
Another user reported the search page being blank with an infinite loading icon after updating.
"KB4515384 should address an issue that causes high CPU usage from SearchUI.exe for a small number of users," they wrote. "But this update again introduces the same problem as the previous update. Part of the problem is a high CPU usage (~30%) and a totally broken search function. Currently, I see no other option than to blacklist this update also to prevent update to reinstall it again and again."
Another user said that their Start Menu had stopped working and that they were unable to access their Action Centre
"Windows 10 especially 1903 is the most bugged OS ever," one user wrote. "I suggest stay at 18362.295 as long as possible or until all flaws will be finally fixed."
Users on Microsoft's Community forum also reported an issue connecting to external USB devices.
"After the USB HID device issue after September 10, 2019 - KB4515384 (OS Build 18362.356) windows update, my HID device is no more recognised," they wrote. "It is listed by the usbview.exe application but the application I use to manage this device cannot see it."
IT Pro has contacted Microsoft for comment
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Bobby Hellard is ITPro's Reviews Editor and has worked on CloudPro and ChannelPro since 2018. In his time at ITPro, Bobby has covered stories for all the major technology companies, such as Apple, Microsoft, Amazon and Facebook, and regularly attends industry-leading events such as AWS Re:Invent and Google Cloud Next.
Bobby mainly covers hardware reviews, but you will also recognise him as the face of many of our video reviews of laptops and smartphones.