your post does not indicate harsh engagement and does not indicate you have noise.
the only indication on the post is that it slips periodically.
the only thing that comes to mind is the cleanliness and the preparation prior to the clutch disc and the adjoining friction components ( flywheel and pressure plate). given how sloppy most "mechanics" are, the most likely cause was that the friction components were either touched with oily hands or the pressure plate was not rinsed off of the corrosion protective l on the pressure plate.