Well I wonder if you did not have a squib load.
No powder, and under charge or fouled powder that caused the gun to not extract bvecause there was not enough powder to move the slide.
When you ejected the empty cae nad checked the breach I was suprised and cringed to watch you shoot the last two thinking that you may have had a projectile in the barrel. and depending one where in the barrel you can buldge it where the slide will not come back.
Next time, please be safe and unload the mag, and stick a cleaning rod through the barrel to make sure it is clear and protect your self and your firearm.