Prusa, I3 Mk2.
The test model printed fine prior to installing Marlin 2.0.3. It's not the slicer or GCode. I tried several models, and all of them worked perfectly prior to the update. The video below shows what's happening. The Z axis homes, then when the heating is over the head centers, and rises to 15 mm (as shown on the display). The print starts, the head doesn't move down but the display shows 0.1 mm. I know I missed something in the Configuration.h but I can't figure out what.