Try re-loading the page and waiting a minute or two.
If the issue persists try closing browser tabs and trying again.
You can also try returning in 5 minutes to refresh the page.

Why is this happening? The server or your browser may be having trouble calling the large array from a local node. I am looking into ways to fix this and make it faster.

Check to see you are on the Main Ethereum Network and not a Test Net.

Two reasons:
1. Running this site costs money.
2. To slightly discourage the ability of one person to dominate the canvas.