This happened again, unfortunately at an inconvenient time. I was on vacation at the beach with a beautiful view of the sky. However, the DC wouldn't connect up with my Android again. Since I was on the road, I didn't have a laptop or a means of messing with the AP/STA settings.
I got it home and looked at it over the serial port again. Same problem. wlan0 wouldn't connect until I did
sudo ip link set wlan0 up.
This time, I edited /mnt/conf/etc/network/interfaces.d/wlan0 and added
post-up ip link set wlan0 up to the configuration. Assuming I don't switch the AP/STA setting at all, hopefully this will keep the connection working.
I just think it is ideal to use the STA mode, so that the DC can report status to status.outernet.is. But I guess that isn't actually important, as the DC is most useful with there is no Internet connection of any kind. But I thought it was worth reporting anyway. This could be a problem if trying to hook up the DC to a stand-alone wireless network, at a school or something.