I have upgraded my computer using a core i5 2500K from Windows 7 x64 to WIndows 10 x64, and the whole system runs fast and reliable, with one exception: after booting from SSD, which takes only about 10 seconds, my keyboard is really slow for the first 1 or 2 minutes right after booting. "Slow" means that when I start notepad, and type some characters, it takes a second for each character to appear on screen. Everything else is fast, including mouse movement, starting programs, only keyboard input is that slow. After 1 to 2 minutes, the keyboard suddenly behaves normally again.
This happens with every kind of keyboard I connect, no matter if I use the legacy PS/2 adapter, or USB.
Does anybody have any idea what might be the cause of this strange behaviour?