ok i found out the issue, the issue is coming from the modem which does not support IEEE 1905 therefore decos are unable to communicate with one another. This is a drawback on the deco series which...

@Gamester17 did you by any chance manage to configure the m5 decos in AP in a mesh network ? this meaning all decos are connected straight via ethernet backhaul to a switch and not over WIFI Backhaul?