Season doesn’t end with the weekly reset. It ends about 4-5 hours before that, while the game is still up. The moment you see your ratings greyed out, the season is officially over, and you’re in the downtime until the ratings reset and the new season starts.
It sucks but it is what it is. I was 2700ish CR in shuffle in a positive lobby when it happened, I hoped the matches would be shorter, but alas. Next season it is for me.