Hi,
I have the latest version of Interstellar and Real Plume installed along with the latest version of Steam KSP. Without Interstellar installed when I use the LV-N the engine plume is always on, even when the engine isn't activated. I was able to fix this by removing the Squad/nuclearEngine.cfg from Real Plume and restarting. However, I then installed Interstellar which modifies the LV-N NERV to the NERVA and the plume problem came back. I found another Real Plume config that I though