I will give that a shot now. Thanks for the suggestion 
EDIT: I’m afraid that didn’t work either. Have you possibly been watching YouTube tutorial series where they teach you how to make a copy of Braid (the game)? The guy on there uses “MoveRight” too but it is just a custom binding so the name shouldn’t make a difference (I tried to change it anyway and had no luck, sorry).
One thing I have noticed while debugging is that if I attach my horizontal input axis to the working vertical ‘AddMovement Input’ (like the image bellow) then it still doesn’t work which means that it has to be the ‘InputAxis Horizontal’ part that is broken. If how ever I rename my horizontal mapping in the project settings then I get a warning in the player controller blueprint saying that it can’t find the mapping that I’m referencing. Which can only mean that when spelt correctly it is successfully referencing the binding in the project settings.
Doesn’t make an ounce of sense to me why it should work as it is pretty much an exact replica of the other one that does work.
Doh!