Niagara Particle Issue

I have run into an issue with Niagara (Unreal 4.27). The particles in the editor look like this:

However when I play the level, this is all I see:

The particles emit from the plane but I seem to have messed up something to get the result shown when played in-game.

This is the basic editor level for testing with nothing else in place to affect it.

Any advice would be appreciated.