Loading CZML locks up Cesium

I’m using the simple Hello World.html file (attached) from the first Cesium tutorial. I’ve modified it a little to have it load a CZML file (attached) showing the GPS constellation. It finds and loads the file, but after it loads, Cesium locks up with the scene pictured above. I can press buttons on the top and move the slider on the timeline, but the window scene is unresponsive. There are no console or network errors that I can see. Any ideas what’s going on here?

HelloGPS.html (1.06 KB)

GPSCZML.czml (348 KB)

After I posted this I restarted the web server and it loaded fine. I’m using Node.js, I’m not sure what caused the server to fault like that.