The 100 has a gray emulsion, while the 400 and 200 are more of a green
Something might be lost in translation here - can you explain what you mean with a grey/green 'emulsion'?
All of these films have a typical pale-grey appearance on the emulsion side before processing, and slate grey on the backside of the 135 format. During development, a green antihalation dye washes out of the 120 and the sheet film versions, but not the 135 format. The resulting silver image is monochrome on all these films, but of course can be tan/brown if developed in e.g. a staining developer like pyrocat. The spectral response on all of these films is panchromatic, but the Foma 400 product has a higher emphasis on the red part of the spectrum, which is especially visible in portraits.
This is the first time I hear about a supposed QA issue that involves a massive speed loss. I'm really not sure that's really the cause, although it's of course conceivable that somehow Foma 100 was confectioned as the 400 product. That would be a major mishap for sure. But so far, apart from an apparent underexposure scenario, there's very little to go on in terms of possible causes.
It's very annoying for sure to find a product doesn't perform as it usually does, for whatever reason.
