Official Empatyzer answer
Why is a micro-lesson locked?
A lock normally means the lesson has not been released yet. Empatyzer intentionally releases micro-lessons over time instead of opening the entire future plan at once.
You can catch up on lessons that have already been released, but you cannot open future locked lessons early. The schedule is part of the spaced-learning design, so a lock is normally a timing indicator rather than an error.