From time to time I find myself having a face that I can’t use the edge-loop tool on; why?..
Also - is there different types of faces? [I’ve heard the word “ngon-face” used]
Yes there are different types of faces; triangles (tris) with 3 vertices, quadrilaterals (quads) with 4 vertices, and n-gons with 5 or more vertices. Loop cut tool cuts edge rings that only exist with quads.
In your case it’s either an n-gon where the cut stops or you have an unconnected edge. Going to guess n-gon since there is no black square in the middle of it.