Quick answer: Unreal Niagara mesh emitter set to billboard mode not facing camera? Mesh renderer's facing mode separate; set on the Mesh Renderer node.
Smoke particles set as billboard; mesh renderers face an arbitrary direction.
Set Mesh Renderer Facing
Mesh Renderer node > Facing Mode = Billboard. Mesh faces camera per-frame.
Or use sprite renderer
Sprites face camera by construction. Skip the mesh-billboard path.
Audit per emitter
Each mesh emitter's facing mode. Default may not be billboard.
“Emitter facing and renderer facing are separate. Both configured.”
If your mesh particles face wrong, the renderer's facing mode is the suspect. Document.