As the heading says, after spending a few frustrating days trying to get my randomly generated planetary systems to work, I came to realise the problem is a bug with rotating components (and it’s very easily replicated).
This tooltip makes complete sense. Only it’s wrong. The pivot doesn’t create a new centre of rotation, it creates a centre of orbit. This is not a minor distinction and makes this component actually quite limited in its use. All of the documentation I’ve seen supports the tooltip as this components intent, and if you want to create an orbit, then you use the relative location as a radius…
Anyways, to replicate: Create an actor. Add a scene component and make it root. Add a sphere/cube. Make sure everything in the transform (bar the scale obv) is zeroed out. Add a rotating component. Set the pivot translation to 250 units in whatever axis you want. Set the rotation rate to 90 in that same axis. Slap your forehead really hard if this has wasted days of your life 
So I went and wrote my own per tick event to calculate my orbits, and it is not performant at all (I haven’t looked into not ticking when not on screen, which the rot component does automatically). It’d be kinda nice to have this working as it’s supposed to…