Mine just dropped in and had ran 100%KKM barrels can require some fitting, their dimensions are slightly different for a tighter lock up than stock. I believe they offer a fitting service where you can send it to them. If you want to try something before sending it off, polish the feed ramp really well and try another magazine as well. I guess there is also a small chance it could be some weird combo of recoil management/lighter slide/spring, in that case order some different weight recoil springs and see if one works (18/20/22).
Both mine did as well, g20 and g29, but occasionally they don’tMine just dropped in and had ran 100%