It is good that you were able to solve your issue. My materials were fine, though. The solution for me was to disconnect “owner” from SpawnActor. I thought it would be helpful to have an object reference plugged into that, for a cleaner data reference. It seems that “owner” is only used for server replication, and shouldn’t be concerned with single-user experiences.
The stage build/packaged project worked after that. The PIE was always working.