“Context cannot be used while the model is being created” exception with ASP.NET Identity

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The problem was that we were NOT using the factory pattern that MS recommends.

You can use Factory implementation to get an instance of UserManager
from the OWIN context. … This is a recommended way of getting an instance of
UserManager per request for the application.

As a result, “the same context instance is accessed by multiple threads concurrently,” because several requests and thus threads shared a DbContext.

This following is correct. It creates a new instance of MyDbContext for each call to the UserManagerFactory function.

UserManagerFactory 
= () => new UserManager<IdentityUser>(new UserStore<IdentityUser>(new MyDbContext()));

The following is incorrect. It look similar but does not create a new instance for each call to UserManagerFactory. It is what we were using, ergo our site broke.

var userStore = new UserStore<IdentityUser>(new MyDbContext());                    
var userManager = new UserManager<IdentityUser>(userStore);
UserManagerFactory = () => userManager;

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