The person in distress at the "Bandit's Camp" in Velen is bugged for me. I have loaded three different copies of my save, all from various times and each time I've gone and killed all of the bandits, including the leader and looted all of them and everything at the camp but there is no key.

Upon doing some research it seems that this is a result of having gone to the camp previously. It was already on my map and no longer a question mark so I must have run by or something and now going back I cannot get the key.

Just as a test I tried the console enabler mod and gave myself all the keys and even that didn't give me the key to open it.

I have the same problem