Thank you! This is it - the problem was that at https://developer.apple.com/account/resources/identifiers/list → my app, I had to check WeatherKit not just in Capabilities tab, but under App Services as well!
During the beta I had only Capabilities checked, and that seemed to work until Friday, when apparently the check for App Services was activated.
Everything is working now for me :).
Topic:
App & System Services
SubTopic:
General
Tags: