This happened to me when I first built up my conversion. What happened was that I was running a 13 tooth cog and my lockring was too tall, keeping the chain from sitting all the way into the divits of the cog. Pretty slim chance that the same thing is happening to you, but check it out.

- Definitely tighten your chain, but not too tight. You should be able to move it up and down at least a centimeter at it's loosest point.

-Tighten your chainring bolts. If a few of them are loose, then your chainring could wobble side to side, causing chain to fall off.

-Tighten your cog/lockring. I don't know how this could create a chain jump, but just do it anyways.