Heres whats going on in a simple 4 zone scenario.

4x4 C4 Matrix
Sonos 1 in Input 1
Sonos 2 in Input 2

Zone 1 wants to listen to Spotify through a sonos box so they select Spotify on Sonos #1 Perfect.

Someone n Zone 2 wants to listen to the same thing. So they go to zones and add zone 2 to zone 1.

this SHOULD simply add the stream thats being fed to input 1 on the matrix to Both Zone1 AND Zone 2. Sonos 2 should still be Idle

INSTEAD, Control4 GROUPS the 2 Sonos boxes and Sonos 1 feeds Zone 1 and Sonos 2 gets routed to Zone 2.

this doesnt matter much until Someone in Zone 3 wants to listen to TuneIn Radio on Sonos 2 which SHOULD be idle.

Instead, the 2 sonos's get ungrouped, shutting off sound to zones 1 AND 2 so Zone 3 can listen to TuneIn.

Its a major pain because no mater how you select the sources, if 2 or more zone are playing the same thing, C4 is Grouping instead of Matrixing the one box.

Add more zones and more sonos's(Or bluesounds) and the problem compounds.