I wouldn't think 50-55% humidity is good enough for them to shed in. It is good enough for them to LIVE in though. I've only had one bad shed and that was in a glass tank with 60% humidity.

Since moving to a tub and keeping the humidity around 70-80% for sheds has yielded me the best sheds.

In my opinion I would try to get you humidity up to around 70% minimum for shed.