I have the qc 35 ii connected to windows 10 via Bluetooth. Sometimes while I am using it and lessening to a music, I lose the sound for a second and then the sound back again by itself without doing anything. However, I did not lose the connection between them and the connection keeps up.
I am going to guess here that the loss of sound happens only with the laptop and not say when you play music through a smartphone. If that is the case, then the problem probably lies with the laptop and not the phone.
The laptop has to allocate computer/CPU cycles to many things including the bluetooth subsystem which communicates with your QC35ii. Some times it is something you overtly run in the 'foreground' which computes away and sometime it is something the grinds away in the background like a virus check. If the processes on your computer take up too many cycles, your Bluetooth may have to wait and hence the loss of sound.
You can check to see if that is indeed the case by starting your laptop without any programs or background processes running (including no 'drivers') and then play the music and see if it still stops the sound. You may need to use 'safe' mode to test it out.
I can not think of anything you can do on the Bose end to alleviate your issue - the changes need to come from your laptop.