Just found the rounded corners of Smart Stack previews are incorrect. They rendered as circular rounded corners, which are not consistent with other Apple Watch previews and also the physical Apple Watch. They should be changed to continuous rounded corners.
Please make sure to file a feedback with the bug descr and screenshots! If you post back here with the feedback ID I’ll make sure it gets to the right team ASAP!
@Developer Tools Engineer 😄 Thank you for the response! I didn't expect you to pay attention to this minor interface error. I have already submitted the feedback (FB12404233). Thank you once again!