So I’ve being trying out different things to understand more about how attachments works. I’ve more or less confirmed that attachments done in the outliner are indeed lost upon packaging, whether you launch from project launcher or the packaged project. I confirmed it with log prints counting attached items on the LevelCube. While running from the editor, the number reaches 94 actors, whereas in a launched project the number reached 1 actor.
What does work however is attaching the objects on begin play events. The current plan is to tag everything that needs attaching and attach them on begin play. I am worried about a potential initial lag spike, but I have yet to try it out.
I do not know if this is an intended behavior upon packaging. Grateful for any input, and hopefully, these findings helps someone else with the same issue.