Every 3 months or so is a new season for competitive play. Last week started Season 3. In a few months it will be Season 4, etc. This is just for Ranked play. There have been a lot of issues with how players are Ranked and how they climb/fall on the leaderboards so they did a big full reset so they could have clean data to investigate issues to fix for Season 4.
The titles you speak of, you're semi-pro, those change based on your level of earning xp and time played. I think levels 1-9 is Rookie, 10-19 is semi-pro, 20-29 pro, etc. Its totally possible for someone to be level 40 and have the title of Master but still suck and play like a "Semi-Pro" or so.