Did the issue start before the engine rebuild with the original starter, or only after the rebuilt engine was installed?
Is the "new" 2.2kW starter an original Denso, remanufactured or some other brand?
Does the pinion gear/shaft pull out by hand (should be difficult) and snap back quickly...
Is there a shim or anything else stuck on the mating surface where the starter bolts up to the engine?? Is the mating surface machined flat? Do the teeth of the flex plate look good?