Talk:League system/@comment-3974211-20130508011829/@comment-4652200-20130508152322

His MMR is probably too low. If it happens only when he is near 100 LP it's LP clamping, although they claim they've smoothed LP gains to remove clamping...

The low MMR may be due to advancing "too fast" if he is playing Duo with someone in a higher Tier. But playing more games should, eventually, raise his MMR.