I've got you some insights about missing suppliers when adding receipts in QBO.
The absence of a similar detail on the receipt may be the reason why the supplier isn't auto-filled. This occurs because the system will only automatically add a common supplier if the Enable suggested categorization setting in the banking window is enabled.
If it has a similar receipt that was categorized and the supplier doesn't show, we can try clearing the app's cache files. Doing so helps in resolving any errors in the system.
For QuickBooks Online app:
Select the menu at the top right.
Choose Help & Feedback.
Select Refresh Data and Refresh.
In your Phone Settings:
From your phone, choose Settings.
Click on General and select iPhone Storage.
Select an app that's taking up a lot of space.
To free up the storage without deleting the documents and data for the app, select Offload App.
If you get the same result, uninstall and reinstall the QuickBooks Online app. This is to ensure you get the most recent version of the application.
You can also access your QBO account through a web browser and upload your receipts from there.