Once again this is bucking my gut instincts to have a discussion of any import with an anonymous entity, who coincidently happens to be about my age, but your questions have always been good, and you logic likewise.
I can't tell you that vitamin deficiencies are not possible. From what I have seen with thousands of critters, and all the non-fiction that I read (sailing ships of old, etc), I would also say its unlikely. My educated guess is that deficiencies necessary to allow loss of nails would manifest in other obvious and debilitating ways first. As fragile as they are, I can't see it as having much likelihood in chameleons. I have never seen it, where I could even hint at it being due to a deficiency.
As mentioned above, fine metal screen is a long-time known culprit of nail damage and loss. I have often described watching a larger chameleon walk screen vertically as akin to watching a chameleon act as if it has velcro feet walking on counterpart velcro. You are fortunate in that there has not been any secondary infection. If one chameleon is more prone to falling or releasing from screen, it would have a higher incidence of problems than another cham, as you would likely surmise. Sharp claws do not always disengage from fine screen, causing them to snag and be torn out as the chameleon spins or twists unnaturally, rather than a clean release. In the wild, they don't encounter any such surface, and to jump or release is a natural thing. As I mentioned, it is somewhat remarkable that there have been no complications, and the only legitimate excuse I can offer for that is luck !
Wish some of you folks would use the signature option to get a real full name in. I guess I'm old school.
Anytime I found him climbing on screen I would put a bio-vine, branch or other means for him to get around.
