1. A concise explanation of the problem you're experiencing.
Drill-picking certain polygons causes the browser to hang in an infinite loop after upgrading to Cesium 1.39. After reverting to Cesium 1.38, the issue resolves itself and you can then drill-pick things again.
2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.
Rather complex. But this is the loop it's getting caught up in:
Of note, we're not supplying a limit to the function in this particular instance.
3. Context. Why do you need to do this? We might know a better way to accomplish your goal.
4. The Cesium version you're using, your operating system and browser.
Presumably all browsers. Have seen it in FF56, FF57, Chrome 61, and Chrome 62.