Hi @RolandasR, what issue with Spotify volume do you have?
I meant the volume control of lullabies. The app is set to lower volume during the specified time until it is off. It works well if the lullaby is played on phone but it doesn’t if I play them on TV. Lowering the volume manually from phone just works fine, but the app cannot control it, although it displays a bar at the bottom of the currently playing lullaby. The phone volume bar has a cast symbol on it, so perhaps, the app needs to set some option and it would work as well.
The lullaby volume controls the media sound stream. Is the Spotify casting via a different stream, when you connect it to the TV?
I tried both. You can stream from phone or start playing standalone on TV. In both cases volume control on phone changes to casting mode, perhaps Spotify knows when it is played on TV. And Sleep as Android sees it as playing in both cases. But it cannot control the volume then.
You can use TuneCable Spotify Downloader for Android to download the Spotify tracks you want to your Android phone. Then you can set the downloaded Spotify audio as the ringtone.
Feel you on the unpredictable playlist shuffle, waking up to random tracks you haven’t touched in months is not the vibe! 
While Spotify’s direct integration can be quirky, a workaround some of us use is downloading playlists locally and setting them as custom alarms.
If you’re open to a manual approach, tools like Tidabie Music Go make it easy to save Spotify playlists as audio files (MP3/FLAC). Once downloaded, transfer them to your phone, pop them into a “Ringtones” or “Alarms” folder, and select them directly as your ringtone.