Servers can’t handle Summon Bear ability from the bear tree, retaliatory thorns: “thorn burst”
the problem starts in the arena when enemies don’t die quickly enough and bear is starting to proc hundreds of ice thorns, starting around wave 200 (or even around 120-130, depends on the map), either server is going to crash (lost internet connection) or the game is becoming unplayable, simply online servers can’t handle it