Character keeps sinking into ground even though root motion is disabled

Hi!

I am quite new to Unity and I am having a (probably pretty simple) issue but I can't seem to figure it out.

I have a simple scene with a character that can walk, but with every step it sinks a tiny bit into the ground. It's barely noticeable at first, but after walking back and forth for a while it gets clearer.

Visual. Before vs after running around.

I have unchecked "Apply Root Motion" in the Animator Component, and also tried baking the Y position into pose in the animation import settings, but neither of these solutions seem to work. Also, the character does not have a rigid body or physics whatsoever yet.

It must have something to do with the animations as the issue doesn't occur when the animator is disabled.

Does anyone have any suggestions on how to fix this?

Thanks in advance! Lillian1810

EDIT: For some reason it now randomly switches between sinking down and floating up, so something really random must be going on....