it’s not really a bug
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.