Yeah, this is a bit strange... from what I can see, the white almost seems to be the underside of the leaf? You've got some curling going on?? This may be heat-related stress. You don't have any info on the humidity they're kept at but I'm guessing that it, too, is pretty high. I'd cool things off a bit - temp to the low 70's and humidity (if you're measuring it) to about 50-55 and see if things don't improve. I don't think it's bug-related as you'd see damage done elsewhere (in the middle of the leaf as opposed to the edges)... that being said, keep an eye on those leaves such as the one in the last photo... have you looked at its underside to see if there are bugs there?
Best to you... and keep us posted!