Some causes of failure are:
- The first bath looses strength and leads to underdevelopment
- Different films need different second baths, different pH
(Fuji tends for instance to give greenish negatives)
- Grainy pictures (also because agitation is manual and sometimes we don't agitate enough)
By now, I am getting good results with Fujicolor-Eterna-250D, besides a very tolerant film that can even be developed with hair dye as I already showed here while other films give very bad results.
These pictures have a very good color in just automatic scanner settings and a fine grain.
So, as soon as I have more confidence with the alternative to the split developer, I will make a new post. By now, pacience is needed, but the idea is to include in the second bath a certain amount of the first.