Out of curiousity, what do the fired cases look like? Is there any damage to the case mouths on any of them?

If the slide is not travelling fully to the rear due to limp wristing, you may see the case mouths damaged where they contact the front/top of the ejection port instead of being thrown clear. There will also be brass marks on the slide where the cases are hitting.

Also, as the slide did not move fully rearward, as it starts forward the new round may not be fully positioned for feeding, and catch on the bottom edge of the feed ramp.

This condition can be compounded with a full magazine and drag caused by the pressure from the magazine spring as noted above.

Don't ask me how I may know this...