When playing music background or while screen is locked the music stops unexpectedly and when I look if someone's calling me or something there is nothing. The app just closed completely like it was never opened.
I strongly think that it is deriving from the phone because same thing happens to my friend who's using Xiaomi, so please look into it and update the app
Even if you suspect this issue might be device-related it's a good idea to try running a clean reinstall of the Spotify app on your device. This will get you the latest app version and remove any corrupted data from previous installations.
If this persists after the clean reinstall, then try what happens when logging in to your Spotify account on a different device. If it doesn't occur on another device, we suggest making sure that your device is up to speed with any software updates available.