@Andeh1 While keeping Deco mesh in Access Point mode, force Main Network to run on 5GHz only. You will find this option under WiFi Setting in Deco app: Also, try different speed test apps and sites....

@_pete_ If what you have in your Deco mesh is Deco M4 and S4, you will need to manually install beta firmware to enable that feature, more about it here:...

@SteveWex Thanks. I have different X-series Decos: all X50-PoE hardware V2. I can confirm I have experienced all issues you described, while doing in place replacement of M5/M9 with X50-PoE. Except...

@SteveWex I just did in place upgrade of my M5/M9 Plus Deco mesh to set of X50-PoE. What I thought initially was incompatibility between M5/M9 and X50-PoE happened to be completely different issue:...

@Cornishman Because the problem seem to go away from the Deco mesh itself, I can only give you general recommendations. Things I could have tried myself in your situation. You have PoE switch, just...

@dkw92 Well, maybe you should try daisy chain I suggested. If that gets you Ethernet backhaul, it is not firmware or configuration setting, the focus of investigation should shift to switch and...