Well, it's doing it again even after a software re-install.
the problem is sporadic. Sometimes it prints perfectly, the next time it will leave a few layers off at the end of the print. As a new test, I ran two identical prints back to back. one printed correctly and the next one didn't. and, sometimes the build platform doesn't go all the way down to the fill level from the home position. It lowers down to about 5 mm above the resin level.
Is this a software issue, or, could it be an issue with the laptop computer? It's not a vat or resin issue. It seems to be mechanical.