@Prince.Chiu Hello, please check the compatibility list of Deco M9 plus. https://www.tp-link.com/Deco-M9-Plus/compatibility/ Below is a screenshot. Good day.

@MTA Hello, so the current network diagram is router(bridge mode)--Main Deco--switch--printer/2 computers, the wired devices do not work properly, right? With them connected as mentioned above,...

Still the same, you can return it and get a new one. This time, if possible, you can test its performance at the store first. Good day.

You are welcome, glad to help you. If need more help in the future, do not hesitate to contact us. Have a good day.

@QuimC Thanks for your valued reply. Glad to hear that you fixed it. Congrats. Now you can enjoy the internet with the TP-Link router. Any further problem, please let us know. Best regards.

@Splee How many devices connect to the Deco M5 simultaneously? Please verify whether they obtained valid IP address from the Deco automatically which do not show up under network/online devices list....