R6900P no 5GHz and router takes a dozen of reboot before getting to the UI

Hi everyone,

I got a used R6900P AC1900 and it is not under warranty anymore, I thought it was a R7000 actually as it is also an AC 1900, so is the R7000P.... Seems like the R700P has the same hardware than the R6900P, a stripped down version on the USB ports.

Anyway. When I started it it took multiple reboots to get to the UI. When in the UI, the 5GHz network is dead....

I tried the latest firmware available and resetted the router multiple times but get some weird characters in the  wireless setting configuration.

Anybody was able to fix the issue? If so how?