Maybe there is a incompatibility problem between your fiber lanbox with C9_v3
Contact tplink support that is the best way to resolve your issue.

Check if the router has WAN/internet IP address when the globe led turns red? If there is one, change DNS to 8.8.8.8. If there is no Ip address, save the system log when red globe light turn on and contact tplink support to debug

The connection led changes colour when the router does not receive a dns query response. No dns service and the router assumes no internet connection. If your ISP's default dns server is spotty, try pointing your router to a more reliable on such as 1.1.1.1 and 1.0.0.1list two alternate dns servers on the router's network settings config screen. Leave the two dns spots in the dhcp settings blank.