1. A concise explanation of the problem you’re experiencing.
An extra arrowhead sometimes appears on a polyline using PolylineArrowMaterialProperty. It appears somewhere in the middle of the line and can shift around and appear/disappear on moving the camera. Sometimes it appears while the camera is moving and disappears when the move is ended, but often it persists. For example, here is a screenshot where the extra arrowhead appears at the same time as the expected arrowhead, using the polyline demo:
2. A minimal code example. If you’ve found a bug, this helps us reproduce and repair it.
This can be reproduced with polyline demo here and manipulating the camera position. I’ve had best luck reproducing by rotating so that the arrowhead points towards the camera and then zooming in (similar to orientation in image above).
3. Context. Why do you need to do this? We might know a better way to accomplish your goal.
This looks like a visual bug in the line feature.
4. The Cesium version you’re using, your operating system and browser.
Most recent Cesium, using Chrome on Windows 10.