OK, so I've got an Echo and an Echo Dot and I also use the android app to play in the car.
Never had it so far - but what happens if you try to play on another device (e.g. the echo) when the account is already being used (e.g. android app). Does it disconnect one or warn you?
Also, on my android phone, a lot of the stuff is downloaded (ie. offline music) so its not live streaming - does this make a difference also?
What happens when you try?