For a possible cure, try a tablespoon of Epsom salts in a gallon of water. Sprinkle it over the leaves and into the soil good. Don't drown them, but give them a good watering.

That will supply mg. If you see improvement in a couple of days, then you've found the problem. You can use it each time you water or at least once every other week.

Blossum set might help.
It's calcium something or another,a spray for the blossoms.
Also if calcium is what your plant needs check out a cactus fertiliser.They are usually low on nitrogen and have calcium added.
Habaneros especially like/need calcium when they fruit.
I use a fertiliser called cactus juice when I have blossom drop.Sometimes too much water and nitrogen causes blossom drop too.

What ratio of catus juice do you use and how often do you use it? Also is it safe to use since cacti aren't eatrn like peppers?