The Vista Fusion Engine operates normally, and produces normal amounts of thrust, but while it's operating and producing thrust it has no plume and no audio. There is somewhat of a blue glow coming out of the engine (or rather, being reflected from the nonexistent plume onto it), but that's it.

I can provide a list of my mods if necessary. I do have RealPlume. I tried uninstalling it and testing the engine again, and had the same result. I then reinstalled RealPlume and tested it again, same result.

The Vista Fusion Engine is the only engine I'm having this issue with, so I think I've basically ruled out RealPlume as the issue.

Updated to the latest version of Interstellar Extended, and the issue persists but has changed a bit. There is now rather quiet audio coming from the Vista Fusion Engine, but the plume is just a three purple spheres vectoring out of the back of the engine that get smaller and dimmer as they go on.

I should have mentioned, I'm running KSP v1.3.1 on Windows 7 Professional x64.

should be fixed now