After installing a few recent updates, a Windows 20012 R2 server demanded a reboot. Instead of coming back normally it got caught in a reboot loop with error 0xc000021a. The following was attempted but with no success:
- repair mode
- last known good
- safe mode
Most finds on the internet seem to match XP/2000/2003 instead and provided no help. What can be done (short of a complete reinstall)?
 I'm not 100% in reconstructing this, but according to what my WSUS reports as "downloaded" for that box, I suppose the updates were KB3084905, KB3094486, KB3095649, KB3095701, KB3096433 - just in case that's helpful.