npm run reference/test getting stuck sometime.

While running the npm run reference/npm run test sometime it gets stuck. I did some debugging and found that in capture/genBitmaps.js on line number 88

this.thenOpen(url, function() {......})

the callback is not getting called even after the page is loaded fully.

I tried setting the stepTimeout and not stopping the process onStepTimeout and continuing it fixed the issue.

But just trying to understand what I am doing wrong and why it is happening. Also would like to know anyone else had the same issue. Are there any other better solution to the problem?

My app is a ReactJS single page app. And I am using slimerjs as the engine.