Suddenly , SharePoint stop redirecting to /Pages/Default.aspx if the user don't write the complete URL. For example if the user request only the domain name http://test without /pages/default.aspx it will ask repeatedly for login with no success.
Fix:
- Make sure AAM is configured rightly
- Make sure Everyone has read-only permission in the following folder C:\inetpub\wwwroot\wss\VirtualDirectories\web application (also make sure \_app_bin has the same permission)