This is a known issue in the current build of the Mobile Time Tracker application.

If the notifications are enabled and if you are using Project assignments as First Level Object for tracking time in your org. A notification is sent to the users on their mobile to inform them about the project assignment, and that notification message is shown thrice on the device for the users.

We will fix this issue and show only one message on the Project Assignment in the future releases of the Mobile Time Tracker Mobile app.