It is because Editor takes care about lots of things, and does it silently (no error or warnings, which is really bad). Also when playing in editor everything is loaded, when you run packaged game things load slower. Begin play is not always correct (not everything is always loaded when you have begin play event). And constructor scripts are kind of “editor only”, outside editor they are sometimes unsafe.
It was either crashing or making editor keep stuff stable, side effect is when there is no editor code, some things do bonkers.
And that is why every major feature you should at least run standalone game, and when you have time package it try on different computer.