I guess, i found an incompability between Scatterer and Waterfall. Sorry in advance. See in the picture below. As soon, as Scatterer is installed (tested with Spectra and also with Astronomer's Pack - both the same) the plumes of waterfallized engines tend to show less beautiful flickering shadows around the end of the engine bells. It gets visible as you reach the upper atmosphere and beyond. Here you see the waterfallized Wolfhound engine from stock KSP. @Knight of St John @blackrack