Offset Tool making an extra face that won't allow push/pull

I am trying to use the Offset tool to make a border where i can push/pull the centre, as I have done many times in the past. However, it is creating an extra face that will only allow me to pull and not push along with some other weird geometry. Is there something that I can do to fix this?

Turn on Hidden Geometry and see if there’s some hidden lines dividing the face.