If the factory rounds wouldn't lock you back, then it seems unlikely to be a recoil spring issue. I based the spring assumption on the load you published. Usually it's magazines that cause this, but if different mags didn't do it with commercial ammo, either, then the slide stop may be the issue.
Check that the tip of the plunger (in that little horizontal tube at the top of the left grip panel) that bears against the slide stop is rounded and smooth and not chipped or scored. I would look for roughness on the end of the slide stop lever paddle that the plunger bears against. I would smooth and polish any roughness on either one and put a dab of moly gun grease on the end of the lever. I would check the smoothness and lubrication of the slide stop assembly pin and the hole it goes through in the barrel link. Again, put a good grease or lube on that pin. Polish it if you need to. Since you have a new part coming, there is no reason not to try bringing out the old Dremel tool and polishing tools to see what they can do for you on that lever paddle end and the pin. May as well make it a learning opportunity.