ASP.NET/Identity Error: The entity type ApplicationUser is not part of the model for the current context

In Move ASP.NET Identity store to EF Sql database zoidbergi described an issue similar to that which I’m experiencing, but which was not completely answered. I am receiving the error above when attempting to migrate from the inbuilt .mdf database to MySQL. I am using a Database-First methodology and have successfully created the Entity Model from the underlying Mysql database.

ASP.NET Identity AuthenticationManager vs. SignInManager and cookie expiration

What is the difference between using AuthenticationManager SignIn as opposed to using SignInManager PasswordSignIn/SignIn? I have an implementation using the SignInManager and have my cookie expiration set to 30 days however it seems my web app will randomly expire my cookies far before 30 days. Would using the SignInManager implementation be the cause of this? Should I be using the AuthenticationManager implementation instead?