We think we have discovered the cause of this. During testing with some of our Shield barrels we had a couple stick back in the same position that all these threads have mentioned. Lots of different solutions and speculation and many had sent theirs in to be repaired. The problem we experienced that replicated this exact problem (slide stuck past slide lock and had to "smack" to go back into battery) was that the "neck" of the barrel before the squared chamber had too much meat on the left and right sides where it was pinching. This caused the barrel opening in the front of the slide to grab it when at "full recoil" past the slide lock. Some pistols did it and others didn't depending on if the barrel was too fat, or if the metal wore enough and "smoothed" itself out after it wore a bit. we adjusted our barrels to remove this extra width at that point and have never experienced another hang up. Will post pics in a bit of where the barrel is catching to show.