Yes, the issue is most likely the cookie getting expired. Since you didn't add the custom claims to the user's claims in the database, they are lost on refresh since you aren't adding the claim inside the method being called. You can either add the claim via:
userManager.AddClaim(user.Id, new Claim(ClaimTypes.GivenName, user.FirstName));
or you can move this inside of the method that's called when the cookie is regenerated (by default its user.GenerateUserIdentityAsync).
app.UseCookieAuthentication(new CookieAuthenticationOptions {
AuthenticationType = DefaultAuthenticationTypes.ApplicationCookie,
LoginPath = new PathString("/Account/Login"),
Provider = new CookieAuthenticationProvider {
// Enables the application to validate the security stamp when the user logs in.
// This is a security feature which is used when you change a password or add an external login to your account.
OnValidateIdentity = SecurityStampValidator.OnValidateIdentity<ApplicationUserManager, ApplicationUser>(
validateInterval: TimeSpan.FromMinutes(30),
regenerateIdentity: (manager, user) => user.GenerateUserIdentityAsync(manager))
}
});