Particle System not working in Build - 2018.3.0f2

I have three particle systems - everything works in Editor. Particles don't work in Build though - Windows x64. Have tried all quality modes in the res dialog, have tried explicitly playing each system and nothing. Tried setting sorting order from the default 0, to 1 and also nothing.
Only "odd" thing I'm doing is using an Ortho camera and rendering to a render texture in front of the main camera. But no issue in Editor... any reason they wouldn't show in a Build?

 

Slight improvement: I had them starting off-screen. So I stuck them on screen just to see and now they are all three working. Except after moving them around a bit all three stopped... ???

 

It's like if I move any system off screen it stops working.

 

I got it working by turning the three systems into prefabs and then instantiating them and destroying them as needed. Still wonder why they stop working when I just keep them in the scene, but this works at least.

 

Well, it's mostly working. It works about 95% of the time, but 5% of the time I instantiate the particle prefab and it doesn't play... But I do it again and it works.

Can anybody tell me reasons why the particles would do this? What would make them not play? Maybe I should give them a frame after instantiating and before moving?

 

Thank you, I think that was it. I changed it to always simulate and it seems fine now.