Okay, I'm pretty sure this hive is dead - just not sure why. They only brood I can find is drone - couldn't find anything resembling a queen. There's still the equivalent of 6 frames of honey spread throughout the two brood boxes which leads me to think the bees in there are just robbers from the two neighbouring hives.
What's this white stuff?
Despite doing a formic acid treatment in May, I found enough mites on the bottom board to suspect that's what finally did the hive in.