Another thing thats kind of annoying with FLS is that when you load a project it doesn't draw all the waveforms, you have to manually scroll through the project, look at all the waveforms, FLS stumbles a little and then after thats all buffered, then the track will playback without stuttering.
been using FL since 2002, never had this problem. like if i load a project i can see all the waveforms in the playlist and the track will play without underruns from the get go.
it's worth checking the image-line forums for a solution, or posting about this issue if there isn't one. the knowledge base of that community regarding FL's inner workings is almost frightening