@edvin Watch for threading and Swing integration.  That's where I've seen problems with an AppKit crash and a GTK run loop hanging.  This is even with by-the-book use of SwingNode, JFXPanel, SwingUtilities, and Platform.runLater().
Also, this project is on the front lines for Kotlin/JavaFX integration and may find bugs in the kotlin.concurrent package for example.  The #javafx Slack channel points to this one.
Finally, there is the odd bug in JavaFX itself.  I just had a Linux-only bug accepted involving mnemonics.  Even though TornadoFX wouldn't itself fix something like this, it would be helpful to let new users know any underlying issues right away.