Zombies seem to go for the target that is the nearest and once they have acquired a target they seem to switch targets too easily.
Situation 1.
Player A shoots gun 20 m from zombie. Zombie goes into aggro state and their sight and hearing is increased. Zombie will detect from the corner of their vision another player or hear something behind them or in a building and they will lock on to the other target. Zombies also seem to skip the search phase of aggro when they switch targets and they will go straight away to the new target.
Expected behavior is for the zombies to be more interested in the loud gunshot and for them to fixate on it a little.
Situation 2.
2 or more players and a zombie in an aggro state. The zombie will be aggro on player A. Player A backs up and now player B is closer. Player B backs up and player C draws aggro. What ends up happening is that the zombie will just run in circles, constantly switching between targets.
Expected behavior is for the zombie aggro to stick more and for them to not switch targets as easily.
A zombie running into a new player is an acceptable target switch. Original target not in sight but a loud gunshot is an acceptable switch.
Constant switching because someone is barely closer is not ok.