I have a denon S-900w and was having a similar issue. My problem was:
At first I had no problem connecting to the dot and streaming to my denon. After a week or so, the dod would start to disconnect for no reason, then it would sometimes re-connect, and other times it was unable to. After a while, it wouldn't connect at all to my Denon. In fact I couldn't even re-pair the device after "forgetting" it. Finally I did a factor reset on my Denon. This did not work, then I did a factory reset on my ehco.
After the factory reset on the echo, I was able to pair and connect seamlessly. I haven't had an extended duration test of playing music yet, (this will be the ultimate test to see if the problem is solved). But for now, I was able to connect better after the factory reset, so I would start there.
My bet is there is a problem with the compatibility of the bluetooth device chips, but this is just speculation and unconfirmed.
Hope this helps