I couldn't setup a breakpoint
There are other ways to debug. For example, you can add "Browser log" action at the start of the function, and into the "For each projectile" event. Open the browser log in preview (F12) and you'll be able to see when these events are triggered.
Once the enemy fires the projectile, the turn switches to the player and this should automatically stop the projectiles but they don't stop immediately,
It's hard to guess without the project file. One possible reason is that the bullet is created and the turn is switched in the same tick. Instances that have just been created may not be accessible in other events. You need to add a small wait (at least "Wait 0") before switching the turn.