Sivir Shield and Cass Ult bug
These are two bugs I found while playing on China server so I'm not sure if this applies to all servers... But they were both very obvious.
Sivir: I watched her shield absorb both a Blitz pull and a Lux ult when they both hit at the exact same time and were dead on target. Obviously those are both pretty significant abilities and lost us the kill. There were no minions or other champions around so it was extremely obvious that something caused two of those abilities to be negated instead of just one, but she had no items
or summoner spells
to do it. I have seen Lux ults pass through champions before so this could be the case here
Cass: I ulted an Ezreal
facing towards me so early in his ult that no one knew it had started, but the audio for it could be heard while he was stone and then the ult just appeared out of his body. It was really frigging ridiculous to watch, so whether it's intended or just a bug, his ult shouldn't be given such a huge privilege when other abilities and ults with cast/channel times can be cancelled by CC immediately