@David-TP My existing setup is Unifi Modem (dlink, model DPN-FX3060V) > TP Link AX6000 > TP Link Mesh X90 (as AP). Wanna set BE85 as the main router, directly connecting to Unifi Modem. For this new...

@Elffy I switched back to my previous setup that AX6000 as router and 4 units of X90 as AP. It is no problem. That means no problem with the Unifi Modem.

@dimsumcookie having the same problem as yours. I bought 3 units, all Deco has been tried but failed, LED turned to solid red. Calling the support, no one pick the phone as well. Spent so much money...