Don’t take it as absolutely true, I may be wrong on this, but I’m pretty sure this isn’t a bug:
This might be because spawn node is somewhat latent… And functions can not be latent, they must end their functionality within the same tick… Besides, it needs to be sure the object you are calling the spawn from is on the level (actor) to spawn another actor. It takes the level in implicit reference.
But do not despair, one way around it is to implement a Spawn Actor event either on GameInstance or GameMode, and then call it on the FunctionLibrary, this way you can still spawn from function by delegating the spawn functionality to one of these sure-to-be-in-level classes