Certain recipes in Krastorio 2 are circular and allow productivity, creating a "zero input, but existing outputs". I'm guessing causes issues for the matrix solver.

Specifically, coal liquefaction + coal filtration. See screenshot here: https://i.imgur.com/BVI74Uj.png

When trying to remove the zeroed line (heavy to light cracking), the solver asks for another free item.

The problem has nothing to do with productivity module.

When product X is made from a main recipe and another recipe has it as byproduct AND there is enough byproduct to satisfy product X requirement in the floor. Instead of the leftover byproduct be labeled as byproduct, it will be "consume" by the main recpe negatively (so it produce the main recipe ingredient by consuming the main recipe product).

The fact that any recipe can be negative and invert what it does is a problem in itself.

When this problem arise on subfloor (subfloor product is negated) the whole subfloor will be marked as making things on the top level floor despite all factory inside being negative)

Made a proper bug report with a save included : https://mods.factorio.com/mod/factoryplanner/discussion/62f82e69c19ed12ad1eca7a6

Appreciate the reports.