My SP did that too, was crud under the ejector star every time.
This is what I was going to say, except that my SP101 fiveguns have not experienced this, but several of my sixguns certainly have. This is not cartridge-specific, nor brand-specific; I have experienced this with .357 and .41 Magnums, and with Ruger and S&W revolvers. A new, tighly-fitted gun is more susceptible, because it takes less unburned powder or other crud to gum up the works. Oil under the extractor star makes it more likely to happen, as pieces of unburned powder and other crud will stick to the oil or other lube.
In my duty sixgun days, I learned to keep an old toothbrush in a back pocket when at the range, especially during all-day training classes.
When Ruger cared enough to make the very best, in the early GP100 days, grunge grooves
were milled under the extractor, to minimize the chance of crud tying-up the cylinder.
This NOT necessarily a maintenance issue; a tightly-fitted, clean sixgun, plus a batch of dirty-burning ammo, can mean this starts during the first reload. When one dumps the cartridges, crud falls from the chambers onto the extended extractor star, and when the extractor springs back into place, the crud is trapped and squished, but if there is enough crud, it prevents full return of the extractor.
Keeping the muzzle vertical during the reload does not totally prevent the problem! Some unburned powder crap falls from the front of the chambers, forward of the cartridge cases. In theory, holding the muzzle vertical makes it more likely that this loose crud will land on the extractor star, though there are other really good reasons to keep the muzzle vertical during the reload.
Premium duty/defensive-type ammo tends to burn cleaner than cheap range stuff. I have never experienced this problem when burning up older carry-duty ammo
