I had this happen to me.
All the impeller blades were intact once apart, it spun the plastic hub in the rubber.
My theory is the vanes sort of "stuck" to the housing after drying out, then upon restarting the hub to rubber bond gave out. I'm sure a shotty impeller (was a Merc) perhaps also.
Seems every time I've taken the seawater pumps off after they have been run in the water then sits a while and the impeller is dry, it's damn near impossible to spin the pump by hand, if so it "pops' the bond loose or I have to spray water or soap in to even get it to spin.