One rivet is not quite right and should be drilled out.
The steel shaft in the rivet pushed the drill bit to the side and created a slot.
This was fixed according to instruction by Zenith Tech Support--install one rivet on either side--halfway to the next rivet. Install a large rivet in the elongated hole.
This rib left a slight indentation (the flash makes it look deeper)--it was smoothed out per Zenith Tech Support's procedure of working it out between a block of wood and a spoon.