That looks like an ldaps cert change on whatever DC is handling the login for your scrubbed out AD user.
Skyline is a bit basic in that never expects the cert it recorded when you installed AD auth to change, and spits out this error when it does. Going in as the local admin user and updating the AD config should fix it until it breaks again.
Tough if you're using LE based certs that update regularly. It's a shame this problem has never been seen before /s
