The model I'm using is subdivided and mirrored. Here are some pics of the problem, both the solid form and the edit mode. enter image description here

enter image description here

  • $\begingroup$ First, duplicate the object, then apply the mirror, so you can see what your subdivision is working on. After that, notice anything? You have a highly non-planar 6 pole. Search for subdivision topology-- you'll find that sources recommend against 6+ poles, and even non-planar 5 poles are to be avoided. $\endgroup$ – Nathan Apr 6 at 23:12