Perhaps I’m crazy, but I’m completely confused about how to scale mesh particles in Niagara.
If you set the scale, the previously displayed mesh will disappear.
This scales the size with a factor using Particles.Initial.Scale - if you didn’t set that in the spawn script then it’s scaling a zero value.
You can always check what variable the renderer is using for the size by looking at the bindings and then set that variable directly or use another variable.