I don't think it's fit, since I did 10 000km last summer on the same bike same fit. the only thing that changed is going from mountain bike pedals to road bike pedals. Way less float, so I think that's the issue.

I did talk to a lawyer at my firm who used to be a nurse. He suggested that it's likely just a lot more stress on the outside of my knee because of how my foot was positioned all day. I did move my cleat a little closer to centre, so hopefully that will be the solution.