Not really enough information to go on, so I'll toss out a few possibles.
Have you made any recent changes to the gun?
Is this a stainless gun, and if so, when was the last time it was cleaned and lubricated?
Has anyone worked on this gun?
With the slide stop installed and the barrel pushed down and back into the frame... what is the gap between barrel ramp and the frame ramp.
What brand and quality are your magazines? Metal or plastic followers? Are any or all of these magazines "extra capacity" (meaning 8 round) flush fit magazines? They are notorious for nose-diving the first few rounds.
Have you taken any of the rounds that didn't feed and check them for bullet setback? In simple terms, the bullet should hit the ramp and glance up and into the chamber. If the bullets are setting back, they are absorbing some of the energy needed for that process to occur.
Note the location where the bullet nose hits the feed ramp... is that area of the ramp particularly rough, or covered with copper or lead? If so, remove that contamination.
That's all I got... which is (mostly) typical common issues.