I figured out my own problem.
Apparently Edge Loop does not work properly then there are higher subdivisions present.
I did a Del Higher, hide all but the geometry that I wanted to make an edge loop for and clicked on EdgeLoop. ZBrush gave me exactly what I expected, a nice clean new edge loop.
I’m happy to have figured it out. I am not happy that it won’t work on stuff I have already sculpted on. Of course there are plenty of ways to get around it.
Hope this is useful to someone.