I have to say it does NOT shoot down the waterborne wax and grease remover not being out of the film before paint. 20% more humitity could be a HUGE factor in this. Think about it, the water in the W&G needs to evaporate, where is it going to evaporate too? Into the air is where, if that air already has a ton of moisture in it, the bus is full, it can't get on!
There is always the "perfect storm" where many very small things add up, without the extra humidity, everything else the same, no problem. With the same humidity and leaving the surface 5 more minutes to flash off, no problem. See what I mean, without the perfect storm of both these conditions, no problem.
I am not saying for sure of course, I don't know, but it can't be discounted. This was a very odd failure so the real answer is out there somewhere in the cosmos.