Our test SharePoint 2013 environment, which is a mirror of our production environment, recently stopped allowing anybody to log into site collections in the content web application. Every attempt to do so results in the message "Sorry, this site hasn't been shared with you." I am absolutely certain that I should be allowed to access sites in that application because a) I was able to access them before the weekend, and b) I am explicitly added as a site collection admin in Central Admin.
One thing that was recently changed in our test environment is that we set up a default AD sync connection and ran a full import a couple of days ago. The import ran without any errors, and I was still able to access everything in the web application after the import.
In my head, I'm trying to somehow connect this to something with claims based authentication. Can anybody offer advice on why this might be happening, or thoughts on how to resolve it?