From what I gather there is something wrong with the compile order of the very first compile Unreal does as it opens up.
I always get a warning that “Projectile Core System is not a child of Mother System, cast would always fail.” error that only occurs whenever I open the editor.
Since Projectile Core is a child actor of Mother, I do not get the error in my other compiles.
I tried literally everything but, creating the blueprint even from scratch does not help. Copying does not either. So the only option I have to create everything from scratch, which is also not something I cant do anymore.
Just my 2 cents.