For several months now, every time any of our 3 Windows Server 2012 R2 domain controllers reboot, they're unreachable for an hour according to our network monitoring software (PRTG).
I can see from the event logs that the Security Accounts Manager service does not start properly with event ID 7044 (The following service is taking more than 16 minutes to start and may have stopped responding: Security Accounts Manager).
Then nearly an hour later, I see event ID 7043 (The Windows Modules Installer service did not shut down properly after receiving a preshutdown control.)
We've got plenty of other 2012 R2 member servers all installing Windows Updates in a timely fashion - it's only those servers with the Active Directory and DHCP roles installed that take an hour to reboot.
I've Googled this on several occasions and haven't come across anyone else experiencing the same.