I recently installed a light dimmer from Lutron / Caseta and it works fine in the Lutron app. However in the ST app when I try to add device, by manufacturer then Lutron. It says “link account”. When I click this it comes up with a dialogue asking what home and room to assign along with a next button. There is the little wheel spinning suggesting that ST is doing something however it never completes and the screen is frozen and won’t accept input.
Do you have another device (tablet or phone) that you can install the ST app and try to link your Caseta account?
There have been similar reports lately so you should also report it to Support and let them investigate,. In the app, go to Menu > Contact us and send them logs.