Thanks to the advice here, I rebooted twice, waited about 15 minutes, installed, rebooted again and it finally was installed.
No USB devices were attached at any time and yes it is an actual ac-1900p as bought from best buy
I am trying to install the firmware on my ac-1900p and I upload the firmware to it, it seems to accept it, reboot and it's still the same stock firmware.
Any hints on what I am doing wrong. I am using the AC-68U firmware like the site says to