Niagara emitter stops activating

I have a Niagara System with 2 emitters
I activate it with a very simple BP.

Both Emitters work fine until I with rapid continual activation. but if its not continual one emitter ('fire") will stop working.

Any help would be very much appreciated?

Not a fix, but you can avoid deactivating the system on Begin Play by turning off Auto Activate on the component in the BP…

Can’t see all your Emitter Update settings, I’ve tried with Burst or Spawn Rate on the first template “Directional Burst” from UE4 4.21, didn’t have any issues.

I did notice if the Niagara System window is open on my other monitor when using PIE, it’d auto activate & loop (so best close that window).