@ImtiazAli 

Thanks for the reply

I hear you

I tried it, didn't work. 

And why did it connect to the Guest Network then ?

main

guest

I have plenty of IOT devices with only 2.5 with no problem, they choose the band. and i even have a 2016 ZTE phone with android 8 that connects to my wifi

Any other suggestions ?

Thanks!

  @Vassilis 

Set password for Guest Network exactly the same as it is for Main Network. If Redmi won't connect to Guest Network after that, take careful look at password and special symbols in it. Start 'simplifying' Guest Network password till Redmi connects again.

If Redmi can connect to Guest Network with same password as Main Network, the password is not the issue.

  @Alexandre. 

Thanks, i know about this kind of bug, now the fantastic is that my main wifi password is a long password with nbo symbols, it is a sentence with no spaces.

The gues password is a complex with all kind of symbols and yet it connects !!!!  This is amazing !

The difference i see is the main is a hidden network, although again i have older phones connecting.

I will try to unhide but it screwes some other connects after hiding it again.

This is totally weird!