FLStudio stopped working" appeared. So I had to manually crash FL by left clicking. Black screen appeared when FL got closed, since OBS had to register the full window of FL.
Hope this better helps (it works on any pattern ...
FL that first had FLEX I think, if not that one then a recentish one. What happens is that when a song is saved as a new file (not saved to an existing file) focus is lost on the fl ...