Especially with Windows 10 and Oracle Java 1.8 you might notice that the main window is suddenly almost completely white or black and you need to restart YajHFC to get it working again.

Usually this looks like this:

This seems to be a bug in Java with the Windows native "look and feel".
To work around this issue, set Options → General → Look&Feel to "Metal" or "Nimbus".

See also YajHFC issue #47.