Deco mesh Ethernet satellites drop offline in fixed-WAN mode

The most likely cause is that the satellites were still set up for the old cellular setup or are not getting an IP address from the new main unit after the WAN change, so their wired backhaul has nothing to connect to. I can't confirm this for your exact firmware, so treat these as the most likely fixes, in order. 1. Make sure the satellite is plugged into a LAN port on the main Deco, not the WAN/internet port. Satellites must connect to a LAN port. 2. Power-cycle everything: unplug the main Deco and all satellites, wait 30 seconds, plug the main unit back in first, wait about 3 minutes, then plug in the satellites one at a time. 3. Open the Deco app on your phone, go to the device list, and check whether the satellite shows as online. If it is listed as offline, tap it and choose Remove, then add it back through the app's "Add a device" option. 4. Check that the main Deco is in Wi-Fi Router mode in the app (Settings, then Network or Operation Mode). Mixed modes can leave wired satellites stranded. 5. Check the cable and port. Try a different Ethernet cable and a different LAN port on the main unit, since a loose or damaged cable is a common cause. 6. If you use the FTTH modem or ONT as a bridge, confirm it is in router or DHCP mode so the Deco receives its WAN address directly. If it is in bridge mode with another router still active, that can conflict with the Deco. 7. Update the satellite firmware from the app if an update is pending, then reboot again. If none of this works: capture the satellite's status in the app (screenshot the device details page) and contact TP-Link support with your firmware version and a description of which steps you tried, since the satellite may need a factory reset or the firmware may have a known bug.