On Thursday, 13 April 2017 11:20:34 CEST Michael Lange wrote: > Another thought: if that is possible, have you tried to boot into a live > system, just to rule out a hardware issue?
I had used Apple Diagnostics to perform a hardware check, and nothing wrong was found. After that, I tried and reset NVRAM, a nonvolatile random-access memory that Macs use to store certain settings like sound volume, display resolution, and (I realise only now) startup disk selection.. and GRUB doesn't start any longer, it boots up directly into MacOS. After that, I also reset the System Management Controller (SMC) and at least now the initial bootup phase into MacOS is much quicker. Now I managed to restore GRUB, using the rescue mode option of my installation USB stick. Everything is as before: very slow keystrokes response in grub, integrated keyboard and mouse working after some time in login screen only when external usb mouse and keyboard plugged in (both of them!) I've noticed that also Apple Startup Manager suffers from the same issue that GRUB has: I press keys and it responds after tens of seconds! Trackpad is also very slow or doesn't work at all. I need to check my updates on Apple side..