You do not say where you grow this plant but in my opinion, this type of damage is caused by an environmental event with water in the leaf crown at the time. Hot sun or freezing temps with standing water in the leaf axils create a "home" for damaging bacteria which will then cause this necrosis. Sometimes only a few opposing leaves are affected with the bases still clean; more often the center leaves are the ones lost.
Take a new, double edged razor blade and carefully cut off the affected leaf just below the dead tissue if only a few outer leaves are affected and the base of the leaf is clean. I use a diagonal cut for appearance sake. If the center crown leaves were affected, then use the razor blade and cut the entire growth down to clean material and dust with cinnamon. This should solve the problem but in the future, avoid watering late in the day or allowing water to remain in the crowns of the new growths. Increasing the space between plants or improving the air movement in your collection would also be beneficial.
Cym Ladye