1. A concise explanation of the problem you're experiencing.
I'm getting and instanceIndex error when removing polylines. This cause seems to be from this issue https://github.com/AnalyticalGraphicsInc/cesium/issues/4983, but I'm not quite sure if it is something that can happen due to misuse of the framework's code. I don't see anywhere in our code where we directly call PolylineCollection.update() btw.
2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.
3. Context. Why do you need to do this? We might know a better way to accomplish your goal.
Create and remove polylines without error
4. The Cesium version you're using, your operating system and browser.
1.49.0