It's not the impeller when working, it's when it isn't. The water drains from the pump and the impeller dries out. It then sticks to the pump housing and breaks the next time you run the genny. Same thing happens on engine
impellers when a boat gets hauled out. When the boat splashes a few days later the impeller need to be replaced. I have a similar problem as my engine(s) impellers are above the water line (catamaran, shallow draft).
I don't know about your impeller face plate but I installed a small fitting that allows me to put a spoonful of oil
into the pump before starting (if not run for a week). The fitting screws shut, seals
so no water leaks
out when running. It has saved me a fortune on impellers. The Globe "RUN-DRY" impellers also lasted longer. JMO... but you can ask at boat yards about impellers breaking when boat splash out of the yard. Very common problem.