Do you have used the MAC clone function?

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.

thallesalmeida wrote I have the same problem. I upgraded to version 180125 and can no longer change the region or language. How much do I try to downgrade to the previous version of the error: 5533....

I guess you need contact tplink via hotline. It seems that there is something wrong with the 5G wireless chip, isn't it? kenhwa wrote same problem here , very problem this tp-link archer c5400 , WiFi...

Maybe you can contact tplink support via hotline.

Maybe you can contact the tplink and let them know your suggestion