Hi. I followed your advice, the one you said stupid simple and boring. in addition, I reread and illustrated them all in my mind (so basically I'm was becoming a robot for that moment) one line by one line.
Then I discovered my own programming mistakes that the engine itself ignores it (It even does flawlessly in the editor). It was that the turret was trying to shoot a non-existent, recently
queue_freed object, that caused a chain problem:
-) A particle doesn't know where to appear
-) Turret keeps aiming THAT target
-) and so on and so forth
Reworked turret's code and everything works flawlessly.. for real. This is the most terrifying bug I have ever made that I was so close to giving up Godot. This is such a relief that it was my mistake, not Godot.
Thank you very much for your effort. I really appreciate it. Your advice worked for me.