@tecoholic If suspect is Ethernet cable, the Master Plan would be to connect either one or both Deco not through that cable directly. This might solve the problem by having device other than Deco...

@Gurry TP-Link released beta firmware for Deco M4(V4) that allows to manually select where Satellite Deco should connect: https://community.tp-link.com/en/home/forum/topic/581554 You only need to...

@Amano7 If you want tri-band, you can also choose from Deco X68 and X90. They are tri-band and based on same WiFi6 technology as X60, so if you are OK with X60 performance - Deco X68 and especially...

@Amano7 You will not need to reset everything, if you are replacing Main Deco. Add new Deco as a Satellite, then promote it to Main Deco and all your Deco mesh network configuration settings should...

@tecoholic This still could be a cable issue. The cable might be just barely good enough for Decos to establish Ethernet link, and ocasionally they fail to. You can do two tests to check that theory:...

@Gurry I am surprised your 2nd floor Satellite Deco has strong signal to Main Deco. Usually, one floor is OK but connecting through two floors is often too much for WiFi nodes. Depends on floors...