The W7 machines (3) here have recently required a repeat log-in, when booting up.
This happened just once on each machine, but seeing it occur on each machine in the last ten days seems more than a coincidence. These are independent machines with entirely different hardware and different W7pro / home versions. They aren't networked, but share a modem through a router. No hardware changes in dogs years.
This isn't a double boot with a restart that windows sometimes enforces after an update. None of the machines is supposed to allow windows updates without human intervention, but all 'important' updates are usually permitted, when presented.
RL