No guide numbers on Yr6 U5 numberlines

Hi, my son is doing 6th grade math on Khan. It's going great. But he's just hit a major snag.

For 6th grade, unit 5, the task is to place numbers on a number line. The problem is that no number guides are visible, each 'tick' represents an arbitrary length (not just 1 unit), and the only way we can find to get it right is with a lucky guess.

I'm a web dev and have looked at the page source, and there don't appear to be any numbers for the chart. I've tried it in Chrome, Safari, and Firefox. Any suggestions?

In the sample image below, the ticks were 3 units apart. One was on 0, the other on -3.

¯\_(ツ)_/¯

Cheers