To reproduce this, run HelloWebView and load the following page:

HelloWebView https://blogs.oracle.com/

It will render a portion of the window and then become unresponsive. A thread stack dump shows that the JavaFX application thread is spending most of its time in com.sun.webkit.Timer.twkFireTimerEvent

Very infrequently it will render more than just the top of the page, suggesting that isn't isn't deadlocked, but rather in a tight loop processing timer events.

This is not a recent problem. I've tried several version of JavaFX and they all behave the same way.