When you use "Enemy has LOS to player" condition, this picks all enemy instances that have LOS. For example, if you have 10 enemies, this event can pick 2 of them. Everything you do inside this event, will only apply to those 2 picked instances. So you can tell them to chase the player, using Pathfinding behavior for example.
You can add another (inverted) event "Enemy does NOT have LOS to player", this event will pick the remaining 8 enemy instances. You can stop their movement, or something like that.
It's a good idea to define an instance variable on the enemy, for example, State. For chasing enemies set State="chasing", for other set State="patrolling", this will give you more control and allow you to distinguish them in other events. So your code can be something like this:
Enemy has LOS to player
Enemy State="patrolling"
Enemy set State="chasing"
Enemy find path to player
Enemy on path found
Enemy move alone path
Enemy does NOT have LOS to player
Enemy State="chasing"
Enemy set State="patrolling"
Enemy Pathfinding Stop