I have the same problem as several people in this thread: When streaming music from Amazon Echo to RPI3/M2P, the Squeezebox server stops after 3-20 minutes. After disconnecting and reconnecting the BT link it works again for some time, but then it stops again.
When I stream my Amazon Echo via BT to an Ubuntu server not running M2P (with a loop from BT input loop to HDMI audio output) everything is stable for hours!
My assumption is that there is a bug in the M2P BT plugin! Whenever there is a short BT connection problem (which can always happen due to WiFi interference) then the plugin stops working.
@heiner: Did you ever test your BT plugin with Amazon Echo running for several hours with a Wifi interference from neighboring access points?
Thanks and regards