SharePoint 2013 "Sorry, something went wrong. An unexpected error has occurred" when users Sign Out

After we upgraded from 2010 to 2013, we found internal users are not able to consistently login to the two web applications with the mixed authentications. Different internal users hitting different web applications on different Web Front servers at different time might get the different results as we described in previous blog.

In additional, users are getting the same error when click “Sign Out”. The error is in the following screenshot that is identical to one of the errors we described before.

The exception from the ULS log is also same as we reported in previous blog.

Unexpected       System.ArgumentException: Exception of type 'System.ArgumentException' was thrown.  Parameter name: encodedValue    at Microsoft.SharePoint.Administration.Claims.SPClaimEncodingManager.DecodeClaimFromFormsSuffix(String encodedValue)     at Microsoft.SharePoint.Administration.Claims.SPClaimProviderManager.GetProviderUserKey(IClaimsIdentity claimsIdentity, String encodedIdentityClaimSuffix)     at Microsoft.SharePoint.Administration.Claims.SPClaimProviderManager.GetProviderUserKey(String encodedIdentityClaimSuffix)     at Microsoft.SharePoint.Utilities.SPUtility.GetFullUserKeyFromLoginName(String loginName)     at Microsoft.SharePoint.ApplicationRuntime.SPHeaderManager.AddIsapiHeaders(HttpContext context, String encodedUrl, NameValueCollection headers)     at Microsoft.SharePoint.Application...     

The procedure to reproduce this is simple.

1. SharePoint 2013 farm have at least two web applications with mixed
   authentications. One FBA with LDAP and another window with AD.
2. Login to the site using window user account
3. Click "Sign Out" and you might get the error
4. Try to login the site again and you might still get the same error

The strange behave is users will stuck on this page even try to refresh to login to the site. Although I have provided a workaround, we still need to find permanent solution from Microsoft.