I have the full size. Never had an issue with the gun before the recall trigger work. After, however, is another story.

The slide is failing to complete battery at least once per magazine. It could be the first round, the last, one in the middle, doesn't seem to matter. A quick push on the slide resolves the issue.

I have 4 magazines and the problem is happening with them all

The only ammo I've used in it the last 2 years is a bulk buy of winchester whitebox, so haven't compared to anything else, but ammo from the same lot never gave me a problem before the recall.

Anyone else had similar experience? Guessing I'll have to contact SIG but maybe someone has a suggestion

It needs to go back. Not much else to say, really.

With a problem like that and one specific type of ammunition, my first suspicion is that the failures are due to how the extractor interacts with the cartridge case in the chambering stage of the firing cycle. I don’t know what the “upgrade” would have done to the extractor or breechface unless the extractor was replaced for some reason, and that’s possible.

You could send it back, but the first thing I’d do is try different ammo. Keep in mind that if you send it back the first thing someone is probably going to do is test fire the gun as it’s received. If no stoppages are experienced with the type(s) of ammunition used, it’s going to be a “no problem found” response. If you don’t have problems with other ammo and even if you decide it needs to go back, at least you can say it’s a problem with only one type, and that’s still unacceptable.

I would also carefully inspect the extractor to ensure it’s not damaged and which might have happened during the upgrade work. I imagine that it was removed during the process and it’s also possible that a different one was installed at the time; perhaps no effort was made to keep the original extractors and slides together.

Even if the extractor is not damaged it’s possible that some sort of tolerance stacking is at work. A tight extractor and slightly oversized cartridge case could cause the problem you’re experiencing.

WWB is notorious for issues. Shoot it with something else and see what you need to do.

How many rounds through the gun, and how is your recoil spring?