It doesn't get out of the way of the next round fast enough and it's a toss up it will jam long ways when the bolt slides forward (to chamber the next round), or, the next round will get in place, but because the case is still in the receiver, they both jam together side by side.
It’s short stroking. The bolt isn’t coming back hard enough to eject the case.
Try cleaning out the gas port and oiling the bolt. It’s also possible your chamber is too tight and the case is hard to extract.
Also check the extractor spring. The extractor might be slipping out the case before the ejector is hit with the empty case.
What a minute. You did say the next cartridge is feeding out of the mag with the empty case in the way. The bolt is going far enough to feed the next round.
Check that extractor spring. The extractor is letting the case go before it hits the ejector.