Many large chain rings (especially those on triples) have groups of teeth that aren't quite as tall as most of the rest. There is typically a group of 2-3 teeth aligned with the crank arm, and then another group of 2-3 teeth about 180 degrees from there, on the opposite side of the ring, that are shorter, or that look ground-down or chipped. This is sometimes found on the middle chain ring also, but most commonly on the largest. They're made this way to facilitate shifting.

Your local bike shop should be able to get it adjusted so that shifting is improved.