Explanation:
1. User is able to login but can't see Case Records --> "Configure Mobile Settings on Case Entity Level"
2. Users can open cases but cannot see the subject of the case - "configure mobile settings at the field level within the case form
3. User reports that they cannot access the system from Dynamics 365 mobile app --> Configure a security role in the mobile permission set of the appropriate user
https://docs.microsoft.com/en-us/dynamics365/customer-engagement/mobile-app/set-up-dynamics-365-for- phones-and-dynamics-365-for-tablets