2000 D LMC Curiosity About Zinc.

I'm not an expert at errors, but I believe that the zinc is starting to really show through, especially on the reverse

I've run across this on other coins Obverse and/or Reverse. I'm wondering how did the zinc bubble mostly copper?

I haven't studied this, so this is just a hypothesis. Zinc is reactive. In many cases the planchet is somewhat porous so in the washing annealing process some water or other chemical starts a reaction with the zinc. Forming a bubble, since the copper is thin it stretches over the bubble. Other issue could be zinc rot coming through the posting or environmental damage. I've had zincoins in a 2 by 2 wiry no zinc spots stored in a low humidity environment get random zinc zits. Since the coins that get the zincs are treated the same as the ones that don't, the issue happened before I got the coin, my feelings are that the Lincoln zinc cents won't last long, do some CRH you'll see what I mean, a circulated copper cent looks circulated but is still in good shape. Circulated zinc cents look terrible with black spots and corrosion.