Illustrator :: Exporting To JPG - White Turning Transparent

I have an A3 sized times 3 artboard file that I want to save out at 300ppi so that I can print it at A1 without losing much quality. I do this every couple of months this will be the 4th time or so. Each time I run into this same problem and kind of just fudge my way around, but I'm not having as much luck this time and can't move forward to printing.
 
each sheet is a series of 20 coupons or so like seen above but when i export to jpg some of the coupons come out like this:

the white layers (there are two) both go transparent and the background paper image leaks through. as you can see in the after shot, in the upper right, some white is preserved (the shadow in a link file, but the white under 408 is an illustrator shape)
 
I've tried changing the white to 1%k or 1%c 1%m 1%y 1%k and things. usually fiddling with it like this in serveral random ways gets it to work eventually.