Hi there.
So... I tweaked it a lot, hope it helps.
https://github.com/dupuqub/constructs/blob/master/Shooter.c3p
There are many cleaner cuts to the code and to the actors' hitboxes. I wasn't really sure where was the bug so I had to keep cleaning wherever I could. The bug now is gone, also the other bug is gone (the one that flickered the screen when your mouse got centered).
Also, maybe I found Construct bug while fiddling with your code, so thanks for that.
https://github.com/Scirra/Construct-3-bugs/issues/4047
It may turn out to not be a bug after all, but I'll update this thread when we get the results.
Either way, I'd recommend for you to check the file I posted in the bug report because it shows a very sleezy trap in the ELSE statement behavior.
Best of luck and feel free to ask anything.
Wow thanks so much for the help! And thanks for the tweaks as well! I've been stuck on this for a bit now and I can finally move on now lol. Thanks again!