Drikusniet: Thanks for asking. Yes, you are right in your observation: the first time fresh chemicals was used I had no problem, next time a few flakes and than more and more. The bottles I have used has not been used for other chemicals, as far as I know I started using them for C-41 the first C-41 set of runs I did more than 2 years ago, without any problems (Fuji film that time); and since then I haven't done any C-41 until now with Ektar 100, but haven't mixed the bottles or used them for anything else, each bottle for each chemical and the same for other other equipments used for each chemical.
The company who sold me the stuff is just about to discuss the matter with Tetenal and Kodak, and I'm waiting for what they have to say.
But since the last time I commented on this thread I have started to suspect that something is wrong with the last stage of the process, the stabilizing bath. I have several times filtered the developer and the bleach fix, but as far as I remember, only once the stabilizer bath. When I now did that some days ago, when sending the stuff to the company, I did find "flakes" quite similar to the thing on the film in the filter paper! I don't really know what the stabilizer contain and what it is supposed to do, but Tetenal says that "the stabilzing process may also be carried out days later". I now have one more exposed Ektar 120 film which I will develop within some days and which I will develop, wash and dry but not stabilize before I see what I have. (Last time the sheets looked very smooth and nice when I took them out of the wash, but not as smooth and nice when taking them from the stabilizing bath - but I wasn't careful enough to be really confident with this observation of mine.)