Just took my brand new LC9s Pro to the range this morning, and had this same issue. Took a couple rounds out and it went in just fine, so I too believe the first round was not seated properly.
It didn't seem to like Gold Dots, as I had a couple failure to feed. Winchester and Federal HP worked well as did all varieties of ball ammo I tried. No issues with the extended mags either! Yay!
On my last shot the slide didn't lock back and I got a "click". Decided that was enough (200 rounds or so) before the second cleaning and another round at the range.
Did get a tiny blood blister from that trigger, though.
Love it anyway!
Day 2 at the Range. I fired off another 200 rounds today, with only two failure to feed and that was using Winchester Ranger HP ammo. It seems that two of my mags might be suspect, both stamped USA and one is the standard round capacity and the other is the extended capacity. A little irritated about that plus had a couple of non-slide locks.
I plan to call Ruger to see if there is anything going on in regard to a fix.
Got that stinking blister on the trigger finger again too!