All sorts of aerodynamic and gyroscopic forces can occasionally conspire to stop a prop in a spin. Not a problem as long as it starts again on recovery! As far as I know it's not type specific, the Grobs I fly aeros in will sometimes stop in a spin (and in a tailslide), but start again OK. You could get the engineers to check the idle isn't set too low, or leave a bit of power on as you go into the spin, or try spinning the other way. Have fun
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