I have similar problem. Just bought the system last weekend. I have the 10s and was planning to add more to it if it performed as hoped. What I am experiencing is the slave unit dropping out then coming back a few seconds later. It is pretty frequent. What's a real bummer is, it is right near where we sit most of the time so it is quite jarring. We are using an echo dot connected via Bluetooth most of the time. I have the speaker that drops,literally about 12" from the wireless router. Says connection is "fair". The master across the room says "good". Keep in mind, across the room is a whopping 17' or so.
The other strange thing is it doesn't stay in the play everywhere mode if the system goes to sleep. It should be in a LTP mode so when the system wakes up it maintains its last state. The whole reason I got this system (echo and two Bose) was for sake of ease for my wife and kids that aren't going to pull out a phone to communicate with the system. I want them to be able to get up in the morning and ask Alexa to play the morning play list while pouring their coffee and they are off to the races of the morning routine.
Right now they need to ask Alexa to reconnect Bluetooth (gets dropped over night) ask for their playlist and then ask me to connect the play everywhere. Kind of a bummer. So, I often come in and they are listening from just the dot speaker which should make anybody at Bose cringe.
System should stay connected via Bluetooth or at least immediately reconnect once echo starts playing, and should stay in whatever mode it was in last (play everywhere or otherwise).