Does anyone know why this is happening?
Actually you only have one face (made of 6 vertices) while it looks like you have two (because you've created an edge from a vertex to another). An edge loops can't go through a ngon so it can't go through that face. So delete the face with X (Delete) > Only Faces, and fill the 2 faces.
What happened? Actually you must have created 2 vertices on the lengths of your face, then, instead of J to join, which would have separated and created 2 faces, you must have pressed F to fill, which has created an edge between the 2 vertices, but didn't create 2 faces, and kept the original face.