From what I recall, the 120 size was dropped because of one component was super toxic and the use of it was banned in Japan, and its function in the 120 was to prevent static marks in cold dry conditions with the paper backing, probably in cameras with a motor drive. I'm not with all certainty absolutely positive that the 35mm and 120 were cut from the same master rolls, but I (me) think this is so, my ancient Fuji Datasheet on Neopan 400 does claim a special anti-static property. Fuji just may have more of the 35mm cut and less of the 120, and have been working to make the Neopan 400 emulsion updated while worldwide stocks of 35mm ran down.
FWIW, the Legacy Pro stocks I got last year (before they ran out) had a much older Fuji production code. I've been shooting Neopan consistently since the 90's so I could reference my own film. I think they cleaned out their film closet, the Fuji/Freestyle deals happen every so often, I recall back in 2000 or so they had a massive sale on real Neopan 400 in 100ft bulk, 18.99 for 100ft, which was half price. I bought at least 5 boxes of 20 100ft rolls over a year for my wedding photography business. I'm fairly certain that Fuji made a small change to Neopan at that time.
But what is the difference between the paper backing of Neopan 400 and Neopan Acros?
Neopan Acros is still available in 120.