SeaDoo 215 hp IC supercharger question

I had your supercharger rebuild service done this winter. Boat ran fine until recently. Surging at 5000 rpm, less than full 8000 rpm at WOT. I wonder if it could be the supercharger slipping some?
I removed the intake hose and I was able to move the impeller wheel with my fingers some distance. Is this normal? My guess is that I should not be able to spin the motor by rotating the supercharger impeller with my fingers.

Any thoughts about this? Thanks,