One last note, hopefully.

I went back to kernel 4.9. The error can still be triggered using the latest
version of VirtualBox with a Windows 10 guest and guest additions installed.
During boot up of the VM, probably when the guest additions are loaded, the VM
stops.

Again I gets the error messages in kern.log and Xorg.log but with kernel 4.9 it
takes a lot longer for the system to freeze. Actually it didn't crash, it just
wouldn't accept any input after some minutes. The mouse pointer was still
moving, but neither keyboard input nor mouse clicks hat any effect. I also
couldn't switch to a text console with ALT-F1 any more.

Hope that helps in reproducing the problem.