@Scampy74 Can you also check hardware version of your Deco S4, I am guessing you got all them as a single set so they should all be same hardware. If not same set, you'll have to check them all. See...

@Scampy74 With firmware 1.6.1, you should be able to see Connection Preference option in your Deco app.

@Cahagg01 As you can see from document I provided that message means Main Deco can't negotiate gigabit speed over the wired link to ISP modem/router, so it downgrades to 100Mbps. Standard...

@Scampy74 There is Connection Preference feature which will let you do that, but it is not available on some of Deco models. Feature is described here: How to select a preferred signal source on the...

@Cahagg01 One more thing. When you open Deco app, do you see "Abnormal WAN Port Speed" message: Abnormal WAN Port Speed. Please Check Your WAN Port Connection

@Cahagg01 I just did same upgrade half an hour ago, my Main Deco M9 Plus is still fine. There is "Test Internet Speed" button on the top left corner of "Network" page in Deco app, are you getting...