After Migration Users Get Access Denied Message

If non-administrator users get “Sorry, this site hasn’t been shared with you” message after your migration process it could be happened because of authentication provider.

So, solution is too easy to implement. You should run below script to change web application’s authentication and migrate users.

$WebApp = Get-SPWebApplication -identity http://<webapp>
$WebApp.UseClaimsAuthentication = $true
$WebApp.Update()

$WebApp = Get-SPWebApplication -identity http://<webapp>
$WebApp.MigrateUsers($true) 
$WebApp.ProvisionGlobally()

iisreset