Woah, this one has me stumped!!! At first i thought it must be the timer so i tried spawning the bullets every x milliseconds... nope still crashes. I have tried toggling all the events off except for the bullet events and it still crashes, so it has to have something to do with those bullets (as you already stated). Of course, it doesn't crash when toggling off the bullet creation event.
I decided to try and make a .cap with the same amount of objects that spawn the same amount of bullets at the same time intervals and it works fine .