If problem is the same with 2 barrels, the slide is clearly not having enough return power to strip a round, fully chamber it and close the slide.

So many things could cause that, friction in the slide, friction in the hammer reset, installed buffer, recoil spring with closed end to rear, sharp inside end on recoil spring scraping on recoil rod, etc. etc. etc.

Without having pistol in hand, I suggest assembling it without the recoil spring and with azoom caps in the magazine, cycle it slowly and feel for any resistance.