Detailed description of the problem:
Yes, I know the Spotify-Plugin is still experimental if there is another Device with Spotify online from which Audio was played last, the Alarm-Audio will go off on that device and not on the Smartphone with Sleep As Android.
Steps to reproduce:
Have another Device with active Spotify online, e.g. PC.
Make sure that in the Spotify Android-App the Playback via Spotify Connect is active on the PC, maybe because you listened to music on that device the day before which makes it the last active device in Spotify.
Wait for Alarm.
Version of Sleep as Android: