Only 4 of 5 Amazon Echo devices found until I asked Alexa to play a song from Spotify

[greaser_geek]

I have 5 Amazon Echo devices - 4 Dots and an Echo. Spotify lists all but one of the Dots as a device to which I can cast music. All of my Echo devices function normally otherwise and are on the same local network. I've reinstalled the iOS app. I've rebooted the Dot. The Dot does not show up in the iOS app or on my PC. If I ask Alexa to Play Songs by Boston from Spotify, it will play fine. Then, suddenly, the device finally shows up in the Spotify App. STRANGE!