Aluminum molds require occasional lubrication. A technique that works well is to have a glob of hard, stick-type bullet lube (beeswax lube will work) about the size of a .45 slug rolled into a football; when the mold gets hot, touch one end to the aligning grooves along the sides of the mold block, on the underside of the sprue plate around the sprue pivot, and on the steel pins along the bottom of the mold block. Use sparingly, if any gets into the mold cavity it will cause wrinkled bullets.
Lack of lubrication will cause the mold blocks to misalign, or the sprue plate to gall the top surface of the mold.