Deco M5 not a true mesh but rather a hub and spokes system
I have M5 with three units. Master, Slave 1, and Slave 2. Slave 1 is 35' from Master. Slave 2 is 75' from Master and gets a weak signal. It is only 40' from Slave 1 but according to the app, only gets its signal from Master. I have rebooted Slave 2 and moved Slave 1 around but nothing changes. This is not how a true mesh network should work. Slave 2 should look for the closest signal, which should be coming from slave 1.
With a true mesh, you could have a master and a line of slaves where each slave would be seeing the closest in the line for best signal. Instead, with the M5, each slave only looks to master for a signal. That is a hub and spokes configuration.