Xiaomi Mi AX3600 without 2,4GHz?

Hello everyone,

I have recently purchased a Xiaomi Mi AX3600 AIoT Router.
But I have big problems with it since its installation.
In fact, I can't detect any 2,4GHz WiFi signal. The 5 GHz appears and disappears from time to time.
I tried to change parameters many times. For example I deactivated 5GHz, or I tried to deactivate and then reactivate the 2,4GHz, but nothing worked. I also restored the initial settings but it wasn't the solution. I updated it to different firmwares but it didn't work neither.
So it's a big problem because the range of 5GHz is really low.
Do you have already experienced similar problems ?
Do you have maybe some solutions ?
Do you think that it could be linked to the hardware itself, or could it be resolved by manipulating some parameters of the configuration ?

Thanks a lot for your help.