PK4 TimeTracker is an online app. That means you need to be connected to the Internet, either through Wifi or through the device's mobile data. If you are not connected to the internet, you might see a blank screen, when you log in to the TimeTracker application on the device.
Please make sure that you are connected to the internet and then re-login to the TimeTracker application.
We suggest you log in to the PK4 TimeTracker application with a good data or Wifi connection. Once the app is synced with a proper data connection, you can Check-In/Out for Job/Project even if there is no data connection on the device.
All the Check-In/Outs done when offline get posted to Salesforce when the device is connected with proper data or wifi connection.