I've looked at other issues similar. What I can tell you is: This program worked a week ago. I haven't changed scenebuilder. A new JRE, as I recall, was downloaded and it is 1.8.0_101-b13. This is on Linux 64bit. In the very same program Lambda notifications still work. I did just upgrade scenebuilder to 8.2.0 from 8.0.0. But I am not actively working on a fxml file.
I believe the only change was a recent upgrade on the JDK/JRE. The default computer is the same release as the default runtime.