This error might be caused by having too much data in your app. Let's try clearing the cache in your QuickBooks app and see if you're able to download those transactions.
Please take a look at the screenshot below:
If the issue persists, you can uninstall and reinstall the app. You can follow the steps below on how to uninstall the app:
I'm including a guide on how you can fix some of the mobile issue.
Let me know if the troubleshooting steps help the QuickBooks app function well when downloading transactions.