Found the solution for Ubuntu 20.04 with DECO M5 Mesh on Ethernet Backhaul (Deco with up to date firmware) I found the trail to the problem on this post:...

Hi guys. Ubuntu in different versions - latest 20.04 - with the same problem. Connection is intermittent with Deco M5 on wired ethernet backhaul. It seems that the mesh confuses my Ubuntu WIFI, which...