This is pretty common with double stack magazines. As long as the magazine doesn't give you any feeding issues, it's nothing to worry about. It is usually just slack between two of the lower rounds in the magazine. Mostly it's because the angle of the ramp on the follower isn't the exact same angle as the feed lips, so the upper rounds are angled a certain degree and the very bottom round is angled another degree, so there is usually some slack towards the front of the round.
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