It's because KK's SpaceX Pack doesn't have a .cfg that expands the plume like for say tundra, if you want it to work with real plume, you should make a .cfg yourself
When I tried to load ksp with rss I got this issue with Kopernicus. I'm not sure why I have gotten this issue as I installed both Kopernicus and RSS correctly.
Image of the warning: https://imgur.com/a/l5mKBMw
My ksp.log: https://www.dropbox.com/s/n9c0jv980myffen/KSP.log?dl=0