>>> I have 2 Echo Dots, and Yes it happens on both.
I would ecpect this, because YOUR BOSE is notifying the Echo to send the music again.
HAVE YOU TURNED BT OFF ON THE BOSE, AND DOES THE PROBLEM STILL EXIST after time has passed? Give us some feedback on this previous question!
How are you turning off the music? Are you telling the Echo to "disconnect bluetooth"? This is what I do, and my BT speakers also turn off BT. When I turn on my BT speaker again, it remembers what it was connected to (if device is on) and the Echo reconnects to it (because modern BT devices can "remember")their connections).