Holes in my mesh that won’t close

This happens often in my works, so I’m sure I’m just doing something dumb. I have holes that appear when I voxel remesh my sculpt. What it looks like to me is that two sides of my mesh are colliding and cancel each other out. But short of actively by hand trying to move the mesh around nothing helps. If I try to add something to one side on the mesh with clay strips the other side gets disturbed too.