Windows server 2012 R@ domain controller and separate file server.
All has been well for years, and just this week when I look at the file server and the shared folders / security on them:
users have the PID ID and a blue question mark
I can not click advanced to turn off inheritance as it is greyed out.
if I add a user, the check name will resolve to the correct user.
Also, I recently had the blue login page where I could not enter a username / password on the file server
Sean Smith