Honestly, I don't ever use Click L3 to change lock on targets.
You push the analog stick in the direction of the desired enemy you'd like to target, then hold R1.
Sometimes, if there are two enemies next to each other in that area - it might lock on to the one you don't want. Simply let go of R1, and press it again and it'll lock on to the target you want. Also, if you want to lock on to a target in the air, simply jumping torwards that target then locking on is an easy way to influence the lock on in that direction.
And lastly, whoever you lock on to - is whoever you fuck up. You don't need to juggle enemy health in any given encounter. You lock on, you fuck it up. You kill it. Then you move onto the next target. Offense is your best defense in DMC5. Managing or worrying about which specific target you want to hit is not what you should be concerned about in DMC games. And by the time you sit there trying to switch lock on targets, you would have killed that enemy already to begin with.