Like Agx had mentioned, Agfa would probably show no interest in how their slide film is working out.
I would say that Maco/Rollei are to blame for the Yellow slide film, Agfa usually sells "Master" rolls to outfits like Maco/Rollei for Maco/Rollei to cut down to user sizes like 35mm or 120, I am thinking somehow the film was mishandled, stored in hot humid conditions, because really old outdated Agfa slide film that was stored badly often renders yellow slides, who knows, perhaps Agfa knowingly sold a bad master roll to Maco/Rollei?
One thing is for certain, Agfa and Maco/Rollei know what has gone wrong and just won't comment, How does that grab ya?
It is great that Wittner-Cinetec has taken the time and effort to make darn sure the master rolls they purchased directly from Agfa Belgium are properly aged and in proper working order to produce color slide and movie film that people will be very happy with, I would bet they have experienced a sharp upturn in sales of 35mm slide film just because of the posts on this forum. Rollei/Maco perhaps now are experiencing a big slump in sales of their CR-200 slide film, who is going to buy it anymore? I guess it will still be good as a "Cross-Process film in C-41 chemistry.
The Lomography folks should be concerned as well because they get their Aviphot Chrome 200 slide film from Rollei/maco as well but only really market it as a Cross-Process film.
Perhaps Wittner-Cinetec might have purchased some second hand machinery to package 35mm film into normal cartridges? Lots of used genuine Agfa production equipment from Leverkusen was sold to Adox and others, Maco/Rollei most likely has some of Agfa's film cutting and packaging equipment.