I reinstalled the plugin Spotty and now the shutdown works again.
It was important to check Spotify Connect in the Spotty settings.
I start the app Spotify with another app called HiFy which connects Spotify with DLNA.
and there was already a connection to max2play (from LMS with plugin DLNA/UPnP).
Now Spotify shows me a new activated Connect to Max2play with which everything runs fine.
Also I don’t need HiFy anymore because Spotify finds the connection to max2play directly.
Thanks for your help and greetings