I can't get to the homepage of my site using just the root url, but it works if I specify the whole path. For example, this works fine:
But the following results in "Sorry, this site hasn't been shared with you":
While on page1.aspx, I clicked the "make homepage" button, and that gives me a success message.
SharePoint 2013 Enterprise, in a site using the publishing feature.
edit: this site has been around for months, and this problem just started today.