When changing the projection on datasets with slews in them, the error OutOfRangeError: Target point more than 0.5 pi radians away from reference point is produces when there is a slew of that size.
I think this is a bug in katpoint that it can come to a sensible answer but a workaround would be set the katpoint.projection.set_out_of_range_treatment to either clip or nan rather than raise in katdal.