Is this rating graph normal? Nearly reached master and then falling back to expert in 5 rounds?

Thanks to Farmer John for his great contribution. He killed me three times this year(two of them were usaco).So sad:(

Anyway this is skill issue.Hope to get better next time.

Link:https://mirror.codeforces.com/gym/104686/problem/F

Actually I have trouble reading the editorial(it's too brief for me to understand),so now I'm here trying to get a more detailed editorial of this problem.If anyone knows the solution,help me pls.