I tested this on my C80 with my Deco's, disabling easymesh on the C80 router does resolve the issue.

@Ache Hi, have a look at this article. https://community.tp-link.com/en/home/forum/topic/697580

@Skydog Deco light can take a while to go green so yeah be patient lol. Cheers

@Richard_M I wouldn't think so, if Deco is on AP mode turn off the wifi on your Bell Giga Hub.

@Skydog Hi, I use BT FTTP with the BT hub and my Deco's in AP mode, I can try and help you. With your main Deco still attached to Fibre ONT (small box on the wall), on Deco App go to "more" >...

@krn07 Have you tried temporary moving the Deco 4 and connecting it via LAN cable to the 1st floor switch, if it works then it would indicate that either an issue with the LAN cable or the 2nd floor...