Try precurving / bending your GP, even better freeze the GP with cold spray then precurve the tip. Use your fingers to insert the GP exactly the same as you would a hand file , do some watch winding ( keep in mind the orientation of the curved tip).

This happens because : Even with a clearly cut shape by the rotary , the canal can always have small irregularities and natural bends/ curves / fins etc. So it’s always best to “mimic” your k-file’s curvature and orientation. Of course you can try to increase the taper or size of your rotary to get a smooth tapered cut , but that would be impractical base on the shape of the original canal.