Southeast of crow's perch and past the boatmakers' hut is a bandit's camp with someone locked in a cage. I've killed all the bandits but I've not found the key in the camp or on any of their bodies. Is this a glitch or do I find the key elsewhere?

Is it the camp near the battlefield filled with gouls and the guy selling safeconduct papers? I think that one is bugged.

No, I've gotten that one. That one is a bit north of the hanged man's tree marker, where you first come in to Velen. Just want to know if I should reload my save and skip it for now if it's bugged. But if the key is found elsewhere (which would be odd), I'd continue.

A lot of people have reported having problems with the persons of interest. Since you have a save, you should load and see if you can get the bandit leader, who generally has the key, to spawn with the other bandits.