The ammunition reportedly used should be fine for all intents
and purposes,we have the effect but the cause is not obvious
the slide locks up on its way to battery and no other issues
are visible.Something is putting the brakes on it.
The extractor is engaged and the round is half way in.
Failure to feed? good catch all phrase.
The tell tale soft metal traces on the slide stop inside tab are
only further indication of the cause,many pistols show them
too and yet do not malfunction but if the slide binds or in extreme
cases stops and the copper deposits are there then the rounds are
most likely interfering with the action.
Investment casting can be extremely accurate but if the tolerances
are loose and they stack up there can be trouble,factory definitely
should not have returned the pistol without resolving the issue.