I seem to recall a similar explanation being bandied about a few years back when Fuji discontinued Velvia 50. Within a year or so, they started manufacturing it again, presumably with a slightly tweaked formulation. If I ever heard an explanation of precisely what happened, I don't recall what it was. It's conceivable that history will repeat itself for Neopan 400, but I wouldn't count on it.
Originally Posted by wotalegend
As to the question you pose, I recall hearing that backing papers need to be tested against specific films, because the two can interact and produce bad effects. If my information (and memory) are correct, then, it's conceivable that the backing paper for Neopan 400 may have been different from other Fuji backing papers. Note, however, that I have no priviledged knowledge; I'm just speculating.