It's very unlikely that you made that spot out of one spline (which would not fill in), but someone will mention it if I don't.
I'm also presuming that that red CP which appears to be a 5th CP in the group is actually in the background.
It's possible that one or more of those CP is actually two CPs in identical positions.
try... this...
deselect all. one at a time select each CP (by clicking, not by grouping) and drag it somewhere else and see if there is still one left behind in the same positions.
I have done this before by "extruding" but not dragging the new CPS to a new postion, then forgetting I had extruded, and extruding again.
Last hope if the above isn't the case... delete the 4 CPs and make them over by extending the neighboring splines.