The wither will only use all its 3 heads to attack players and not entities. So if there is only one player the wither will only use one main head and not use the other two to attack other entities, if there are two players the wither will use two heads and the third head will not be used to attack other entities, if there are 3 players the wither will use all 3 heads to attack 3 players, but these heads will not be used to attack any entities.
Steps to reproduce: summon the wither and several other entities which the wither shoulf attack and see that the wither does not use all 3 heads
Expected behavior: the wither uses all 3 heads, the main head attacks the player and the other two attack both other players and other valid entities.