Originally posted by SubsidedLemon:

If the ground you are trying to level is too raised or too low, the hoe will leave large lumps or divots. To substantially lower a bit of land that the hoe cannot flatten, you will need to hit the bumpy area with a pickaxe.

Or if a bit of ground is too low, you will need to raise it with the hoe’s second function, elevating ground."

Yea this could also be an issue. Certain ground just won't lower/raise via how beyond a certain degree, gotta use pickaxe to lower it or raise ground with hoe to raise it. Though I assume that's not his problem.

There's mods you can get btw that allow you to raise or lower terrain beyond the limit btw.