@Ken_B You said you Main Deco is wired to router. In that case, you can switch Deco mesh to Access Point mode: Switching a Deco to Access Point (AP) Mode After that, check speeds again. If problem is...

@Henkan Let's start with troubleshooting, then. 1. Check in Deco app if Satellite Deco Basement reports Ethernet backhaul, you should see it in Satellite Deco info page: 2. If it does, take Satellite...

@Henkan This helps, thanks. As far as Switch Office concerned, you have both Main Deco and Satelltie Deco (from the basement) connected to it. This is not going to work. See TP-Link FAQ: General...

@Kavan_Williams Archer axe5400 uses OneMesh and is not compatible with Deco mesh. See TP-Link Deco Mesh vs EasyMesh vs OneMesh vs Omada Mesh What's the Difference? This article also provides list of...

@Henkan Well, you gave network layout that does not mention second switch. You ask what could be the problem when connecting Satellite Deco to that second switch. You need to provide more details. To...

@Blufkip It is possible Ethernet link between switch 2 and switch 1 is broken. You should check Ethernet cable and connectivity between these two switches. The following forum topic discusses similar...