For some reason, it's suddenly possible to control Spotify even when the screen is locked. I haven't changed anything, not even restarted the mobile, but yes. Maybe there was an update or something
According to our information, we recommend that you make all updates on the watch and the smartphone, as well as release all authorisations for the watch. If that doesn't help either, then you should contact Xiaomi directly. Here is the support centre in Switzerland: hello@mi-store.ch.