That has happened with me also. S&B ammo.
I tried some winchester and pmc and it would happen again at about 50 rounds.
I changed all my springs with the Wolff M1 Carbine spring replacement set and it would work fine for a while before it would happen again.
My bolt/slide had a lot of slop and jiggled around so I went out to find some replacement parts.
I found a "new" slide on ebay and I found a new in wrap 1956 underwood bolt at a gun show. so far I have not had this issue happen again. I have fired about 400 rounds of Wolf .30 cal and have not had any issues to report.
I would also get ejection problems like this...
and so far I have not had one with the "new" slide and new bolt. I would inspect the extractor, my original extractor was broken, half the "lip" was missing.