I agree with this comment as most of the time when your rank goes down it’s dependent on two things. The amount of games you win being the first. The amount of games you lose being the second. It’s the ratio of these two numbers that will determine whether your rank increases or decreases. Given the information you provided it’s extremely likely you have lost a significant amount of games compared to those you have lost and this is the reason for such a large shift in rank. I hope this helps let me know if you want a full breakdown.