There is a bug in the game if you get the skill for upgrading the skeleton regeneration rate and don't upgrade it, it causes the auto generator to not work
Viewing post in Spirit Dungeons (formerly Soul Not Found) comments
Really? This is my longer explanation: There is a base level of monster generation that happens before the upgrade is gotten for improving the speed of generating monsters. After the monster generator is gotten, that stops because the upgrade program can't handle a value of 0, and because of that, makes the monster generation at 0 speed.
If that is not a bug, explain why it is not one.