Ok this is so annoying. I beat hard mode on free aim to get unlimited painkillers and it didn't unlock anything. I definitely wasn't going to play through that all over again, so I decided to get a gold medal on every level in score attack, so I did, and it didn't unlock anything. What the heck? Is there something I'm missing?

Did it unlock the achievement/trophy for finishing on Hard?

If not maybe the checkpoint was overwritten if you used chapter select by accident.

No it didn't give me the achievement either so maybe that's what happened. Ugh I can't believe I have to do that all over again, it wasn't even fun playing it on that difficulty.