If you experience that the Mileage Book app stops registering your mileage in the middle of a trip it may be caused by your Android device going into power-saving mode. This can result in access to the GPS being blocked. However, this can be avoided by turning off the battery optimization off for the Mileage Book app.
By following this guide, you make sure that your Mileage Book app is never put in battery-saving mode.
Keep in mind that these steps may look different depending on which Android device you are using.
From the Home screen, swipe up and then find and tap Settings.
Tap Menu button > Battery optimization.
Tap Not optimized > All apps to see the complete list of apps.
To turn off battery optimization in an app, tap the app name, and then tap Don't optimize > Done.