Just a reminder for those that want to upgrade...
Before upgrading the new FW, please unplug any device you have on AC87U USB.
Immediately after upgrade, turn off the router by switching off the On/Off button. Press and KEEP pressing the WPS while turning ON the router, until you will see one of the blue LEDs from the front flashing rapidly.(usually it will take around 10 sec) Only now you can depress WPS button and switch Off and On again the router (using On/Off button). Plug again the USB devices - if any.
After this you should enter manually all the settings and start testing.
From my experience, if i skip any of the steps described above, i always ended up in weird/slow performance.
Thank you.