Agreed it sounds like too low of humidity. I would either mist the tank or give the snake a humid hide (filled with Sphagnum moss) when it goes in shed. The hide can be as simple as a ziplock container with a hole for the snake to go in and out (just make sure the container is big enough and the hole has no sharp edges). Sadly it sounds like the tail might be dying (pictures would help). The only thing I can think of to do is help the snake shed easier and hope the tail gets better.