This is a known issue in the PK4 TimeTracker application.
If you are using Project Assignments for tracking time in your org and the notifications are enabled, then you get one message on Project Assignment or changes related to the Project assignments.
But the same notification message is shown thrice in the messages tab, which is a known issue in the PK4 TimeTracker app.
We will fix this issue and show only one message on each Project Assignment or when an assigned project is updated in Salesforce.
The changes will reflect in the upgraded release of the PK4 TimeTracker Mobile app.