Best answer by Airgetlam
If it's the former, you may want to turn off the autogrouping function on autoplay in the room settings for your PLAYBAR, which would un-group the speakers every time you turned on the TV.
If it's the latter, there's something odd going on, and I would recommend that you submit a system diagnostic within 10 minutes of experiencing this issue, and either post the number here, or contact Sonos Support to discuss it. I tend to suggest the phone folks, they have more tools available, but are only available during business hours. Both the Twitter and Facebook support folks are available 24/7.
There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.
In the grand scheme of things, adding a BOOST would only deal with issues with the speakers connecting to your wifi. If your speakers are set up as surround speakers, they actually connect to the PLAYBAR and not your wifi, across a 5Ghz network, and only the PLAYBAR would be using either SonosNet or your own wifi.