As I recall, many years ago in the Glock armorer manual they used to list the minimum recommended velocity for ammunition used in Glocks. While I have no idea what happened to that early 90's manual I used to have somewhere (the newer ones I have no longer list that info), as I recall the lower velocity threshold for a 115gr 9mm load was something like 1150-80fps. I can't remember exactly. I remember being struck by how close it came to the velocities sometimes listed by the ammo companies for their 115gr loads, though.
Check the factory stated velocities of some of the inexpensive 'budget' or bulk 9mm 115gr fmj loads (and remember the optimistic nature of factory ratings and the expected standard deviation that might be encountered), and it's hardly surprising that an occasional low powered 9mm load, using a light weight bullet, might not develop enough power to optimally cycle the slide.
Now, factor in the potential for an occasional 'less than optimally firm' locked wrist and/or shooting technique, and shooter fatigue during a range session ... and you can see how influences other than the low velocity loads might combine to lend themselves to an occasional short slide run or might adversely affect feeding 'timing'.
Why do you think that one of the usual manufacturer recommendations in armorer manuals (and not just Glock armorer manuals, either) is to try different ammunition if a functioning problem is experienced with one brand?
You apparently have determined that the Winchester USA product line works well in
your Glock when it's being fired in
your hands. right?
Nothing wrong with trying other brands (or bullet weights) so you can have alternative choices, but it might be prudent to consider the possibility to find that not all brands ... or all production lots of even a 'favorite' brand ... might offer you the optimal feeding & functioning you desire in
your specific gun.
It's not uncommon to have an occasional low-powered, or even a short-loaded (often called a 'squib'), round slip through production, and that doesn't even take into consideration the potential for an out-of-spec or damaged round to slip through upon occasion (bad primer, reversed primer, no flash holes in the primer pocket, mangled case mouth or bullet, wrong powder charge, etc).
Here's a couple clickable thumbnails of a round one of our folks came across in a box of Winchester USA9JHP2 147gr loads (what folks on the internet like to call one of the WWB loads) during qualification one time.
I've seen similar things happen with even some of the expensive "premium" defensive loads, too, but it somehow seems less surprising when you come across it, or hear of it, happening with a budget/bulk load.
I used to collect examples of such out-of-spec or damaged factory loads encountered as a firearms instructor ... before I figured out that I didn't need to keep all those rounds. Nowadays I just keep a few examples of some of the more unusual or interesting occurrences, and that's only when I bother to remember to keep them.
It can happen at one time or another if you shoot enough rounds.
When you consider that some of the big makers have the capability to produce upwards of 1 million rounds within a 24 hour period, it's pretty impressive that they can keep their QC as high as they do, I'd think.
That's why it's probably prudent to test fire random samples from boxes, cases or production lots (depending on the quantities purchased) of ammunition which is going to be dedicated to defensive carry use, I'd think. I've heard one expert I respect in the field suggest that it might be a good idea to buy ammunition in case quantities, so some rounds from that case can be test fired for function in the user's specific pistol, and then the rest of the case can be kept aside for carry use.
