I have had the same hangup occur on several different S&W pistols. It always requires a reset of the recoil spring guide rod to get the slide to fit.
I would check each part by placing in the frame separately to see how the parts normally fit. Look for burrs or hangup areas.

Sometimes when this hangup happens I just bump the slide and it goes back. That is usually after I reset the spring and barrel first.

You'll get past this problem eventually.

Bruce