AC87U - GUI bug - is it possible to upgrade firmware without GUI ?

Hi !

I guess I'm not the first one to have this bug, but it's like the 8th AC87U I buy and get the same bug...

Is there any other way to upgrade its firmware than doing it through the GUI ?

Screenshot of the problem :



It's the same on any computer/browser/smartphone, even after hard reset.

Any clue ?

Thanks in advance !

Jonas