Also when you say "difficult to spin" do you mean that when you attempt to spin it by hand it seems to resist the spin?

I find that this often happens with electric motors even though nothing is wrong.

For some reason the coils seem to remain energized for a while even after power ( or the battery pack ) has been removed, causing some resistance to attempts to spin the prop.

If you wait awhile it disappears as the ESC's capacitors discharge.

Normally when power is re-applied, and if braking is set to off, the motor will seem to spin freely again.