When adding a niagara system that reproduces a skeletal mesh and a skeletal mesh as components to a blueprint, the niagara system immediately updates its skeletal mesh to the most recently updated skeletal mesh component in the blueprint. This occurs even when the user hasn't added the Set Niagara Skeletal Mesh Component node to the Blueprint's Event Graph or Construction Script.
Since the niagara system's skeletal mesh updates directly after the user updates one of the skeletal mesh components on the blueprint, it will affect the niagara system every time, even if the other skeletal meshes in the blueprint aren't meant to be used with the niagara system. This seems like this would prevent the user from effectively being able to use a niagara system in a blueprint with more than one skeletal mesh.
This also may cause confusion for the user while viewing the blueprint in their level in the editor viewport as it gives the impression that the system will use a different mesh than it will actually be using in the level (depending on how the system and blueprint are setup).
If the user has the Set Niagara Skeletal Mesh Component node executed in their construction graph for the blueprint, I think it makes sense to update the view of the system in the editor since that's how the blueprint is being initialized. If the user isn't using that node or has it implemented in the Event Graph to be executed at runtime, the system should show it's default value to indicate that the blueprint is initialized using that default value until it is changed during runtime (or not changed at all, as the case may be).
The skeletal mesh rendered by the Niagara System is still the default value (SK_Mannequin mesh) regardless of what skeletal mesh components are added to the blueprint
The skeletal mesh rendered by the Niagara System updates to the last updated skeletal mesh component of the blueprint
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-72347 in the post.