Let me help you recover your missing data from QuickBooks Online (QBO) to the mobile. You'll need a strong internet connection and an updated version for it to sync the latest data.
If everything is up-to-date and you have a good internet connection, I recommend clearing the application data to ensure your QBO app works properly.
For iOS:
Go to your phone's settings.
Select General, then choose iPhone Storage.
Tap QuickBooks Online from the application list.
Select Offload App to free up the storage without deleting the documents and data for the app.
For Android:
Go to your phone's settings,
Choose Apps (varies by device).
Select QuickBooks Online from the application list.
Go to the Storage section, then tap Clear Data.
If the issue persists, I recommend uninstalling and then reinstalling the app.