First: Does it happen with UMC,
AND Winchester
AND PMC, or with just one brand? If just one brand, stop using it!
Second: if it happens with all brands, is the gun clean and lubricated? If not clean & lube it!
Third: the extractor may have carbon or brass chips keeping it from working freely. Detail strip the slide and thoroughly clean the extractor and the slot it fits in.
Fourth: the extractor may be damaged, while you have it out examine if for chips on the edge that extracts the shell.
Fifth: The ejector may be damaged.