Hi - after installing 10.13.5 I've had my mouse get stuck for about 10 seconds about every 30 seconds. It has happened once a day for a few days now. Reboot helps, and I've found nothing else helpful. After a reboot it stays away for many hours. System log has this line every time there's a stall: "kernel stalling for detach from iohidsystem". During the stall the cursor and screen updates are paused, including the beach ball. None of the controllers make the computer respond. After the stall, if I click on some window, button or other UI widget, the stall starts again. But not all windows or buttons do this. Sometimes it's Finder, sometimes Console, sometimes the Shutdown dialog, including the Shutdown button itself. Yet I can sometimes click around for 10-20 seconds before one of the clicks makes it pause. It happens exactly at the mouse click. Doesn't matter if it's trackpad or mouse, both bluetooth. It keeps stuttering even after I remove every wired accessory I have. Google and this forum had nothing about this problem. IOHIDSystem is a kernel driver, so very low level Apple stuff. I've booked a call with Apple, but the iMac 5K 2014 is out of warranty, so let's see. Any suggestions or advice? I already know about diskutil verifydisk, SMC/NVRAM reset, safe boot, combo update and reinstall, so no need to mention those. I'll consider them next, but also trying to get some work done in the meanwhile.