S9 Ranks/MMR is inconsistent??

I got placed Plat 3 80 LP for jungle, i won my next 4 games and promoted to plat 2 without losing a single game, why am i still getting gold players in my games if its the new season and i got placed plat 3, havent lost yet but still there are gold players in my game O.o as a p2. my friend got placed p3, lost like 5 games in a row after placements, won 3 games from 0 lp got into promos, won his promos and skipped p2. how come we both got placed plat 3, both solo q he lost a bunch in a row while i didnt lose any yet he skipped and im still playing against mid-high gold players while hes playing the correct ranked players.