https://www.reddit.com/r/leagueoflegends/comments/55lezv/cleanse_bug_shows_up_again/?st=itu82o6g&sh=3e49e1c3

We had a look at the interaction of Cleanse and CC effects earlier today after the Cocoon-Cleanse interaction yesterday. Best we can tell this is how Cleanse has worked for at least a year - likely much longer. That's not to excuse that this isn’t ideal, just that it's not at all a new thing.
Different aspects of the game update at different frequencies. The server generally runs at 30 frames per second, but buffs update at only 4 frames per second. What's happening in this case is that Cleanse's cast is evaluated on the 30 fps cycle and immediately clears CC effects. It then queues up an increase to a tenacity-granting buff count. That increase takes effect on the next buff update, which can happen up to 250 milliseconds later (on average, half that). If a CC lands in that timing window, the tenacity from Cleanse will not be present.
It’s an issue consistent across all champions and use cases, therefore we’re treating it as an unintended interaction. Teams were informed of the details of this interaction before matches today, including that this would not be a remake condition. We will not be hotfixing this as we don’t want to incur the significant risk that a new build brings to an ongoing event. We will evaluate this for fixing as part of our normal release cycle.

3줄 요약하면
- 정화를 사용하고 '3초간 CC 지속시간 65% 감소' 버프가 걸리는데 0.25초의 시간이 걸림
- 그 사이에 다른 CC가 들어올 경우에는 지속시간 감소 효과가 적용되지 않음
- 롤드컵에 참가한 모든 팀들에게는 금일 안내되었으며 추후 수정 예정
(이번 롤드컵 중에는 수정되지 않음)


페이커의 이슈로 인해 라이엇에서 조사를 시작했고. 조사 결과 위와 같은 내용이 확인되어. 월요일 경기 전에 참가팀들에게 안내를 진행했다고 합니다.
수정이 간단한 이슈가 아니여서, 수정시 다른 문제를 만들 수 있기 때문에 롤드컵 중에 수정되진 않을 것이라고 하네요.