Have you tried a different BT device? It could be the BT device, as opposed to the phones. BT should have a range on the order of 10meters (30ft). Since both exhibit the issue, that would be my first impression.
Is the device paired with both phones, so that either phone can connect to it if it is on and the phone's BT is on? Just thinking that there might be a fight between the phones and the BT device cant decide between the two. I know some devices have a primary pairing and some have "a whoever connects first" kind of thing.
Yeah, I tried my LG surround sound at home at the same issue happens. I think I pretty much tried everything down to erasing all my Apps. and still have the same issue. I pretty sure its just the phone, I tried a coworkers S5 to the same BT device and it worked even at a 10 ft,. range
I also tried this and disconnected the BT at home from my Wife's phone and still the same. the BT headphones I just bought those about a week ago and my phone has been the only device paired with those, with the exception of my coworkers phone