Put damp moss in the log. A log is not really a good hide for a ball. A tight hide with one door is preferred. Many types of these are available and they will create a good humid hide when damp moss is added.

If your humid hide is made of a Tupperware like container that has a clear bottom, the bottom may be the reason it is not being used. Try piling substrate around the bottom of the container to black out the inside of the container.