Well a google search told me that Neopan 400 120 had the offending chemical but as I suspected would be the case answered none of my other questions as to whether other Fuji films were affected and if not why not, etc.

However google gave a link to a forum in which eventually someone quoted a reply that he after much effort, received from Fuji. It made no mention of the said chemical but did say that it was a question of economics pure and simple which is the one explanation that does fit all the facts.

Clearly despite the love that afficionados of N400 120 expressed for this film there just wasn't enough of them to make it viable.