Quick answer: Unreal replicated actor receiving state updates before its components are constructed? OnRep functions can run before BeginPlay - guard component access with IsValid.
Client receives a health update. OnRep handler accesses the health bar UI - which doesn't exist yet because BeginPlay hasn't run.
Guard in OnRep
void AMyActor::OnRep_Health() {
if (IsValid(HealthBar)) HealthBar->Update(Health);
}Defensive check; safe before BeginPlay.
Or queue and apply post-BeginPlay
Track pending updates; apply in BeginPlay after init.
Use bReceiveBeforeBeginPlay flag
Some properties opt out of early-receive. Use sparingly; the bug class doesn't justify the framework workaround.
“Replication is async with respect to actor lifecycle. The bug class follows.”
OnRep handlers should be defensively coded by default. The class of bugs caused by 'I assumed BeginPlay ran' is large.