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Running Spotify app on MacBook Air connected to my home WiFi.

Playlists are synced to MacBook Air for offline access. 

Running Spotify app on my Samsung Galaxy Note 4 connected to my home WiFi.

Able to use Spotify app running on Samsung Galaxy Note 4 to control Spotify app running on MacBook Air.

Lost internet access, not WiFi.

Able to use Spotify app running on MacBook Air to play music synced to MacBook Air for offline access.

Spotify app running on MacBook Air is no longer listed in "Show available devices" in Spotify app running on Samsung Galaxy Note 4.

Shouldn't it be enough for the devices to be on the same WiFi, with or without internet access?