Whispersync in the Kindle APP no longer works after 11.0 updates

We already tried deregistering, and since i was now using prime household i had just re-downloaded the book on both iPhone and ipad. The most updated version of the Kindle app is installed on both devices. I read to a certain point on one device but didn’t sync to the other. It only syncs if i read it in web browser (not app on other apple device). Also did hard reboot of phone. Whispersync is turned on everywhere (apps and in amazon acount). I will try deleting the app and reinstalling everywhere.

Try some troubleshooting steps: deregister the device and register it again; delete the book and redownload; forced restart; delete the app and reinstall.