Have you tried to travel to your camp through the map with the waypoint instead of the button on the UI?
I had two characters fall off the map completely and die and they reappeared in my camp. Took me ages to be able to realise the map waypoint to camp and the camp at the end of the day aren't the same. But I was able to go to the map waypoint camp and revive people. So I'd love to know if that fixes your issue too.
