I was indeed serializing it, but removing that SaveGame macro did not resolve the problem. Which function should I use to generate the SGUID:
SGUID = USavior::CreateSGUID(this);
or
SGUID = USavior::MakeActorGUID(this, EGuidGeneratorMode::ResolvedNameToGUID);
EDIT: Seems like it works when I call SGUID = USavior::MakeActorGUID(this, EGuidGeneratorMode::ResolvedNameToGUID); in PostInitProperties() except the constructor. Any idea why?