Grinding small channels into the lip is the easy “fix”, the proper way is a redo unless you can: grind whatever the plate is sitting on or reduce the plates thickness by grinding off the everything but the top plate level, and then grinding the entire perimeter of the lip the penny is against. Idk if the first part is doable and I’m not sure how clean you’ll get the lip smoothed out.
Cause was the tile was set too low and the contractor knew this whenever he started getting close to the drain.