The pawn character is added to APlayerController::GetSeamlessTravelActorList, so it'll be persisted during server travel.
The Niagara component is spawned during BeginPlay and activated manually. When traveling to MapB, it got deactivated, which won't happen if we are using a ParticleSystemComponent. Maybe we need a bWasActive variable to record its state in OnUnRegister, like what we did in the UParticleSystemComponent.
Test Project(4.27 C++): [Link Removed]
Steps to Reproduce: [Link Removed]
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-191318 in the post.