I've done a search on the forums but can't find any posts that are the same issue as mine (plenty of problems with this tool though).
Basically, I'm trying to split my aliens head at different sections as per the video of Jays and it has all been going really good until the split polygon tool now refuses to show me a vert at each of my points where I'm inserting the loop. It's making it really difficult to model.

I've checked that I have no extra geometry, everything is merged that should be and my normals are all facing the same way. I've even tried deleting and re-installing my tool shortcut, shutting down Maya, even shutting down my computer but nothing helps!
What's even stranger is that it works properly on the eye!
What's going on?