I've heard from a Reddit user that the reason the Anycubic Photon prints keep failing is that the arm suspending the build plate actually interferes with the top edge of the resin tank when it tries to zero out, preventing the build plate from reaching the 'zero' position.
The user recommends trying a dry run (no resin), pausing the print run as the plate attempts to hit 'zero', and then seeing if you can slide the resin tank around. If you can't the arm has hit the edge of the tank, and the build plate won't hit the bottom of the tray. Thus, no print.
Time to go test it out.
Edit: It worked! I loosened the screws securing the build plate to the mounting arm and inserted a trimmed piece of plastic needlepoint mesh in between them before tightening the screws up tightly. I re-zeroed the plate, and my print run produced a nice print of the supports for my model.
But not my model itself....
Time to tinker with the size of the supports.