This issue just started happening to me. I noticed several errors in the logs saying it couldn’t compile Blueprint XXX. I noticed that all the functions it was complaining about were functions defined on Blueprint YYY. Blueprint YYY also refers to Blueprint XXX. So, it was a 2 blueprints that reference each other. I have plenty of other cases like this, so I didn’t expect there to be a problem. And things work when PIE and Launching. It’s just StandAlone that fails.
So, to appease the finicky StandAlone, I made an interface ZZZ, which Blueprint YYY now implements and I made Blueprint XXX only have references to interface ZZZ.
The compile errors went away and my project is no longer broken.
Hopefully this helps you.