We now have the following registration modes to help improve the Push experience
Continuous - Use this if your SIP server does not support multiple registrations. The Push server will maintain a continuous registration with your SIP server. The app will not unregister or register.
Standard - This requires your SIP server supports multiple registrations. The Push server will maintain a permanent registration. The app will register and unregister as it moves to foreground and background. This is the recommended mode.
Synchronous - The Push server and app will swap registrations. When the app is closed or backgrounded it will unregister, the Push server will then register and 'take over' the registration
Single Register - This works the same as the Synchronous mode but neither app or Push server will unregister first
Standard is the recommended mode and removes the small window where neither the Push server or app are registered which can happen with Synchronous mode. If your SIP server does not support Multiple registrations then try Continuous mode, if this mode does not work then use Synchronous.