First of all, it would be very helpful, if you reduced your layout to a minimum..This is no small project anymore with 5+ layouts. That makes it hard to find what we need.
A capx that is reduced to the events that are essential for your problem would be nice.
this is the solution:
find this event:
Change it to this:
If you are interested why it didn't work before:
You need a "For each". If you don't use it, the event will trigger for the first instance that meets the requirements and for that instance only.
So if there is at least one enemy that is already below 1 health, it won't trigger for any other enemies that meet that requirement.
You fix this by adding "For each".
But since "For each" and "Trigger once" don't work well together, we will have to find a way to prevent blood from spawning over and over. Be do this by only triggering the event when the enemy isn't already playing the "Dead" animation, thus, not being dead already.