The light does not flash during boot; and is not flashing during firmware update in setup. It just went OUT, but has not flashed once. I saw one reference to O2s not always flashing. This is very confusing for anyone booting a new product for the first time. Needs to be fixed so that all Os behave alike. IF this is a firmware issue, the docs should say so.
General observation: setup on the o2 has been difficult. Multiple failures and restarts. Hangs. Reminds me (not favorably) of the Pine64 and LattePanda machines that I also sponsored. In contrast, my fleet of RPi, Up and Odroid boards are predictable and run reliably. Setup is simple (except for the bizarre os load on the Up).
I do understand that you're just delivering, and it's very busy times. Please have someone take a moment and add a few pointers to the otherwise excellent docs to keep us from spinning wheels on the rough spots.