Access Policy Already Being Evaluated - SharePoint

I'm assuming you mean Access Policy evaluation is already in progress for your session" rather than "already being evaluated". See this post for lots of discussion on that issue:

https://devcentral.f5.com/questions/problems-with-windows-10-anniversary-update-and-citrix-access-49028

The use case is a bit different, but the root cause and workaround is the same.