Before introducing changes to the official League of Legends servers, Riot Games uses the PBE to do tests and collect initial feedback from players. This is where all the new features that are about to hit the game are reviewed weeks before they appear in the patch notes. While the devs are aware that new items can have some issues, they probably didn't expect any of the new items to result in multiple player bans.
The item in question is the Heart of Steel , an item designed for tanks that is causing havoc among players. Several community members have reported being banned after using this item. “Hello @RiotSupport, me and everyone I played with today on the PBE have been permanently banned for no reason. Please help,” commented content creator RossBoomsocks on his Twitter account. with over 800,000 YouTube subscribers and affected by the bug.
Riot Games is working on fixing a bug that has 'banned' many players
Riot is already working on resolving an issue that has already affected many test server users. the situation: "Thank you for contacting us and my apologies for the problems you encountered with the game. (...) I have investigated the matter and it seems that many players have reported the same thing to the time of your report. We are currently aware of this issue and are working hard to resolve it."
This type of situation is why the preseasons are introduced on the PBE just over a month before they arrive on the live servers. Riot Games wants to be especially careful when so many changes are coming to League of Legends at once. And still happy, imagine if this misadventure had happened to your main account?