Model number, hardware version? try to hard reset the modem Make sure the firmware version is the latest one.

Is there anything changed with this router? Make sure you do connect to the main Wi-Fi. Have you tried with another smart phone? your current firmware version and hardware version of Archer C9?

hey, you need to register a TP-Link cloud account. Here is a link for you: https://www.tp-link.com/en/faq-818.html Or you can read more instruction, QIG or UG on tp-link official website. That...

Is it still on the parental control list? or other devices under the list can be still controlled properly? There shouldn't be no any other settings we need to aware.

tried this before.. no success with another usb-c cable consulted tp-link support, they advise extension socket~

It seems deco Wi-Fi system is TP-Link new product direction. They should focus on this product and support them for a long time. Wish they will provide more and more good products and benefit us:)