I've seen this post for a while but didn't know why its happening, but I've just thought of a cause.
I believe normal entities are not rendered if the center of them leave your field of view, so I believe that's what's happening. However I think there's a way to force it to always render (not recommended though). I suggest you take a look at how the vanilla beacon beam is rendered (TileEntityBeaconRenderer) and try something along the lines of what they've done.
Stop your bumping, anyway this is expected behavior from a custom modeled thing although I'm not sure about entity's, their isn't really a way to fix this from what I know, its just because of minecraft's rendering. Trust me, it bothers me too I hope you can find a way to fix this!