Riot Games probably hoped to get rid of the bigger part of League of Legends bugs by reworking Mordekaiser but it appears that patch 9.14 opened a floodgate for a massive torrent of bugs, and some of them are fairly game-breaking.
Mordekaiser used to be League of Legends' biggest source of bugs and Riot Games squashed all of them by completely reworking the champion. After a brief period of calm, the storm has come with the patch 9.14 that introduced bugs ranging from chat being unavailable over masteries that don't work to being unable to enter a game.
The most game-breaking bug was probably the inability to enter a game after accepting a queue, all up until the game starts for everyone else.
This issue affected both League of Legends and Teamfight Tactics. In League of Legends, it could be mitigated through /remake command in ranked mode but Teamfight Tactics doesn't have such precautions yet, which led to many players losing matches due to connecting after the PvE rounds had already concluded.
Chat was completely unavailable for hours, which is something rather odd for Riot and League as such issues either didn't happen or were quickly fixed before.
Then again, it is quite possible the developers found themselves overwhelmed with the swarm of other bugs that they either couldn't decide what to fix first or the fixing queue was too long.
The major bugs have been fixed as of the time of writing this article but it's still worth noting that this was perhaps the buggiest patch in history of League of Legends.
To be fair to Riot Games, they are working on a lot of things simultaneously right now. Patch 9.14 introduced a new champion, ranked queue and balance changes to Teamfight Tactics.
Furthermore, the introduction of TFT marked the first time in history that Riot Games managed more than one game at the same time.