Guys, I’ve fixed the issue! 
So I had an Xbox 360 controller plugged in. Yes I’m using a PC with Logitech X55 input controllers but if you also have an Xbox 360 USB controller plugged in then it assumes the cursor is being used for head tracking and fights the actual mouse cursor.
I don’t remember this being an issue before and I suspect it has been introduced in a recent patch but I can’t say for sure if it’s Sim Update 11. Anyway I’m just so happy I found the issue! 