My Bose headphones can be connected to two devices simultaneously, and paired to more devices (I don't know the limitation for pairing). Same for my 40$ bluetooth speaker.
This happens to me, but usually with my phone on the train; happened this morning, in fact.
But it's also happened with other brands so it's not limited to Bose.
Which would mean it's a Bluetooth issue.
GoNovate G10 is the smallest bluetooth that sits in your ear like a hearing aid. I LOVE IT.