bored about "Error code: 9003"

bored about "Error code: 9003"
bored about "Error code: 9003"
Model: TL-MR6400
Hardware Version: V4
Firmware Version: 1.12.0 0.9.1 v0001.0 Build 190730 RC.59984n


i have this 1 year router / modem which has become unusable.
if I want to use some advanced function of my router (like assigning a static ip to a client) it becomes impossible to do it because this error appears which does not allow me to do anything.
I updated the firmware, did various hardware reset ... but nothing.

tplink support replies to do factory reset or replace the modem under warranty

but he doesn't want to know about fixing this bug

has anyone managed to understand why there is this bug?