Why some players start with 17k? (old question: everything is different now!)

A different system, Glicko-2, is used today, so everyone starts provisionally at 13k. However the system is very sensitive, so rank changes more quickly than in the past. So if you play a few games, it should bring you to your correct rank pretty fast. Here is the original announcement for more details: OGS has a new Glicko-2 based rating system!