Actor BP is visible? If no mesh, add billboard for debug. If is visible and emiter not - check your Timer code with Print String when it should spawn emiter. It printing something?
Try different particle, best from starter content, it working always. Maybe particle settings? I’m not sure you are trying it in PIE or simulating, but you can have particles disabled in view too - barely possible but good to check.
Interesting, thanks for trying it on your side.
Then there might be an engine setting messing it up here.
Will have to try with an empty 4.18 project and try each setting.
Luckily I have clean project open for other reasons so I can do simple test like this. Var 0 location is on floor, map center in my case (text 3rd example or something). With this code explosion will start on begin play not only ctrl, but this is only to simple change, works anyway.