In my desperation I just tried something crazy: I disconnected the NAS from the router, took it to the basement next to the Deco M4 #3 and connected Deco and NAS with a LAN cable. Then I took my...

I have the same problem. My TP-Link router with connected NAS and USB device worked fine, both devices could be mapped via the router's WiFi. Then I bought a Deco M4 for the WiFi, disabled the...