Heat that area with a hair dryer then wipe with a clean dry cloth. If it wipes off it's wax build up if not it ain't, go easy on the heat test frequently to avoid loosening the mylar. Just a guess but dare I say it kinda looks like heat damage from bulbs being to close or the wrong wattage??? Is there 2 bulbs under each insert?
Shining a really bright light through them makes any flaws stand out. A lot like magnafluxing a engine block.