I couldn't remember how/from where I did initial setup, and the AP was resisting my attempts to inform a new Unifi Controller with mca-cli, set-inform.

Anyhow, it was still indicating 'upgrade' mode after 8 hours, and was unresponsive to the reset button, so I power cycled it, then reset to factory defaults, and it associated with a new Controller and completed firmware update via GUI with no issues.

So, I told my AC Pro access point to update from "BZ.v3.7.21" (as per the shell prompt) to  BZ.qca956x.v3.7.49.6201.170315.1111.bin as downloaded from ubnt onto the device with wget.  About one hour ago.  The blue/white upgrade pattern is still flashing.  Is this thing likely ever to return to service on its own?  I'll give it a while longer, but this length of time maybe does not bode well.

AC Pro firmware update mighty slow