QC35 and Soundsport switch audio source as soon as iPhone screen turns on
I have Bose QC35 headphones and Bose Soundsport headphones. Both are connected to my laptop (Windows 10) and iPhone XS (iOS 12).
The following happens for both headphones.
I am connected to both devices, but listening to music from my laptop. As soon as my iPhone "activates" (i.e., the screen turns on for any reason, even if I don't unlock it), the music cuts from the laptop and switches to my iPhone (which is silent because there's no music actually playing). This happens everytime my screen turns on. For example, it happens every time I tap my phone to activate the screen to see the time, every time I recieve a notification (because the phone lights up), everytime I put my phone on the wireless charger (again, the phone screen lights up to tell me it's charging). As soon as I lock my iPhone and the screen turns off, music from my laptop continues playing through the headphones.
Additionally, this usually happens, but not always. Sometimes it behaves as exepected. Other times is doesn't. I can't work out a pattern...
How do I stop this?! Ideally, music would continue playing on the laptop until I pause it and play something on my iPhone (and vice versa).