Please just remove that stack plugin https://www.noble-craft.net/community/threads/plugin-messing-up-spawners.4731/
I thought it would be cool. Since players seem to be having an issue with the plugin ruining automatic mob farms, I would recommend that stacking only takes effect when the mobs have spawned from a mob spawner.
Yeh the plugin has messed up both my skyblock and my survival farms.. i had to remove my skyblock one so i could think of a new design and i just gave up on re building it