@Stekel I managed to stabilize my network. Been some time so not sure exactly what I did anymore. The 2 things I remember where: 1) I disabled IGMP proxy in my router which reduced that phantom usage...
I have 7 M5 units installed as access point and connected through ethernet backhaul. The units keep dropping on/pff from the deco network and as a result it is impossible to do any video streaming...