I just had a very similar experience Max! I was gaming in Windows all day, and when I switched back to Mac OS I got a KP! I don't use verbose but during startup and got to the point when the keyboard/mouse would blink on/off (ya know, normal behaviour), it would blink off but never on, instead KP. Was pulling my hair out as after numerous attempts/hours at troubleshooting, even ruing a b/u OS which KP'd, I got nowhere. I woke up my 'hack from sleep when I got up this morning, checked mail, rebooted into Windows 10 for a few hours, rebooted into Mac OS to check mail then back again to Windows. Nothing unusual. No updates or installs for either OS, yet I got KP out of the blue!
I decided to check the BIOS (again) for anything odd i.e. RAM not showing up capacity or XMP speed, drives not showing, etc. Everything looked unchanged except for CSM support which now had an * beside it. Never thought to scroll down to check the first time as I saw no reason why it would have changed in the first place as there was no signs the BIOS had any errors nor reverted to optimized defaults. I clicked to expand the screen and to my surprise CSM support was enabled! I disabled CSM, restarted and all was good. Very odd as I never have CSM enabled to my knowledge, and even more odd is that the BIOS not only enabled it but (thankfully) was showing me that it had changed with the *.
Long story short did you try disabling CSM if it is present for your motherboard?