@__Nikolay__ Hi I just asked the same question & apparently it's an issue with mesh routers not giving the required hidden SSID the extenders require. I've since found multiple feature requests on...

@woozle ah it's not me then thx. Mesh doesn't even work with a guest network? Seems a bit of an obvious flaw when their website says how it "provides uninterrupted WiFi throughout your home". Don't...

So I just bought an RE300 dual band mesh extender to replace my old N300. Unfortunately despite checking my C7 router supported one mesh it turned out I needed v5 hardware & mine was v4 :( No...