I've had mould growth issues this year too, and everybody who has touched the cheeses has been given the third degree. I have the following advice
1) It's been pretty wet earlier this year on the highveld - so there has been more spore around (it has been a challenge this year to avoid contamination, don't be discouraged).
2) I once made white mould cheese where the milk was contaminated (before being pasturised) and I got an allsorts pink, blue, black like a speckled egg, so you may want to try a different milk source if 3-6 do not work.
3) Do you use Geotrichum candidum and Penicillium camemberti in the make, and do you pasteurise? (all these will boost the the right white growth)
4) It is most likely to be contamination during ripening. Unlike jwalker, I close the containers and am not too worried about moisture, just as long as everything is well decontaminated at the start. For instance, my perforated trays are soaked in dilute peracetic acid directly before being used. I have a clean gauze on the lid to catch the drips from the condensation under the lid from dripping directly on to the cheeses. I say all this because my coolroom is used for all sorts of other processes and I cannot guarantee that vented box wouldn't be an invitation for contamination, and draining the boxes is way too much effort!
5) In addition to the hand san, etc, I avoid opening the boxes in a draft or where dust can drift down (like under cupboards/ shelving) and do not lean over the open boxes. Also check the inside of you cooler/fridge as well, and underneath of the shelving, that pesky black mold hides everywhere.
6) You could try to work out the actual contamination source: are they finger sized/shaped? Are they always drip sized (compare to the condensation size) or sort of "generalised dusting"? do they occur on both sides of the cheese or in the pattern of the tray?