Updating a polygon image frequently

I'm working on a application that was built using Cesium b18. I'm using polygons on the Earth with an image material. The images are updated frequently - they are dynamically drawn using a canvas. The positions of the polygons are also updated frequently so they can be positioned directly under a satellite.

The graphics performance was pretty poor so I updated to b21 to see if any improvements had been made. The polygon images were no longer being shown until I set polygon.asynchronous to false. Now the images can be seen, but the polygons jiggle like a bowl of jello.

Any ideas on how to improve the performance of updating an image for a polygon?