Thanks for the project file, it took me a while to figure out what was going wrong (been a while since I've worked with my own software!) but here's what you need to do:
Output Frame Count = Output Frames Per Second x Emitter Lifetime
So in your case, your emitter lifetime is 2, your desired frame rate is 16, so your output frame count should be 32
That should give you a seamless loop. I'll try and change it so that those settings are updated automatically when you enable seamless looping, as a lot of people keep running into this problem (understandably).
The delay capture thing is a bit of an ugly work around for a bug I haven't been able to solve yet, but I think it's more to do with the engine I'm using. Hopefully I'll be able to avoid empty frames without relying on that eventually.
Hope this helps!