Since you've set up your business as cash basis, the reports in the mobile app should also shows as cash basis.
It could be a performance issues in QuickBooks Mobile App that will resolve by doing basic troubleshooting steps. Let's start by resetting the app data to clear the cache and refresh it into its default state.
Here's how:
Click Help menu.
Click Reset App Data.
Close the app when the process completed.
Be sure to right-click the app and Run as Administrator when re-opening.