NO idea what's wrong, but there are hits that are just joyous and dense and lovely. Then suddenly, I'm tasting what is reminiscent of a burnt coil. It makes NO sense. The good hits have a somewhat "gurgly" (juicy?) sound to the liquid in the tank. The awful hits are dry in terms of the sound of the liquid in the tank.
Alas, you're not the only one, if that's any consolation. @Janusz and at least one other person had similar problems. Vacuum lock or some such. There's clearly something weird going on with that "revolutionary" AFC system. Hasn't happened to me yet, but, like I said, I haven't spent much time with my Fresia.
I'll probably revisit it some time later, when I have more time to play with it. Sorry I can't be of more help...