I didn't even modify my backend for the sample react app I used: https://github.com/aws-samples/aws-mobile-react-sample
I just tried awsmobile push and run, and it works the first time. But the next day I came back, it just says the following:
The stack \'arn:aws:cloudformation:us-east-1:XXXXX:stack/MOBILEHUB-XXXXXXX-Development/XXXXXXXXXX\' in Amazon CloudFormation has been modified outside of the Mobile Hub. This stage \'Development\' can no longer be modified inside of Mobile Hub.
You can click the banner on the top to unlock your stack. Note it may return to the original version of your app.