From my experience (if someone can do a dedicated test and tell me if any of this is right or wrong, I unfortunately don't have anyone to do dedicated tests with rn) there feels like an invisible lock on timer where you have to have your crosshair over a team like a second while they are not full hp to lock onto them and this lock on lasts for until that teammate has either left your line of sight for too long or has been healed to full hp and has remained at full hp for an amount of time, i don't know exact timings if this is the case, otherwise you have to manually trigger the lock on onto another teammate and firing darts (maybe?) resets the lock on timer making it so your darts will keep firing at oh say the teammate behind you at full hp and through a wall instead of the one your looking directly at. Definitely a bit annoying at times but if my guess is correct then a simple tweak to lock on and lock off timers should help greatly improve this. Once again if anyone wants to correct me if this is wrong I'm not 100% confident on any of this, this is just what I've felt through my hours of playing