Investigate further

I saw Tiny Tike running past below the terrain. His name tag was above ground. I see many normal NPC disappear below the terrain or worse re-appear above the terrain and aggro on me while I i am fighting other NPC's. It does not seem to be an isolated issue.

Big Mama Molar, gets stuck under ground and remains frozen in place. If I teleport to her I can see her while I fall to the center of the universe.

Also she gets killed by the pirates near the wooden logs, and my the pirates in the big camp near the road

Add The Mauler to the list of npc's that have gone underground, I guess.

The Mauler is not bugged, you just need to kill several of his familly to have him spawn

Yes, you are right. I did it again, sorry bout that.