Sometimes, we forget that League of Legends works thanks to lines of code, and that bugs can directly impact the show.
That's precisely what's happening here: Maximilian Peter Schmidt, League Operations Lead for EU Esports, just tweeted about a game-altering bug that's currently affecting Lux and Syndra.
Riot have simply decided to disable both champions, in order to prevent any mishaps on stage. Sett, who was just released yesterday, also won't be present — not because he's bugged, but to let players, coaches and teams get used to the new champion.
As you can see below, it certainly looks like some need more practice against him...
The disabling of Lux, Syndra, and Sett should also apply to the first week of the LCS as well, and to all Regional Leagues — should the bugs not be resolved before their respective starts.