I am running 5 Deco M9 Plus units. Four of them are Ver. 2.8 and my main is Ver. 1. They are running firmware 1.5.1 and 1.5.6. Since the update my network is unstable even on units that are plugged in

Since upgrading to the latest firmware. I am getting 500-600mbps download and 700-800mbps upload from the fiber modem to the main Deco. But even when close to the Decos the WiFi is at best 50mbps down