Kindle app frozen

For that kind of problem, if it only happens using that app, AND if you're sure that your device AND that app are updated to their respective latest versions, I suggest that you contact Amazon Kindle Support team and ask them.

Regards

Giulio

Ensure that you have updated your iPad to the most recent version of iPadOS - at time of writing, this being iPadOS 15.5.

Also ensure that your Kindle App has been updated to the current version. A bug, fixed in the most recent Kindle App update, has been known to cause the Kindle App to freeze.