Scale flaking can happen when there has been a previous bad shed. Sometimes it just happens. 55% is the lowest I have ever allowed by humidity to drop. 50% isn`t terrible but it is low enough to produce a mildly crumby shed.

Double check that your humidity gauge is accurate. Remember that dial gauges are 100% useless. Digital gauges are a must. If your not sure, pick up another gauge from walmart for $8.