Ok, I can see it could be another kind of damage. The closer up pics and more light show it has no such problem.
I've seen other pics of your collection and you obviously keep good care of your plants!
I had no intentions to offend you -- I've just received my fair share of dead/dying neps over the years. I really hate to see it happen to other members. In my opinion it is better to get these things out in the open.
I'm REALLY paranoid after I lost near two dozen neps last year to various causes.
You're right, it is not dying. It is much healthier looking than the plants I've seen rot on (and it has none of the other symptoms), so noone should worry about that.