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 ...
FLStudio 20.5 had issues with the Reason Rack plugin. If I force closes the program(after waitng a few minutes) and reload the project it works fine. I think that it happens after I have a program loaded already ...