My understanding of JavaScript is cursory, but my reading of that webpage is the UI is just smoke and mirrors, and it is just waiting for the whole thing to be processed in a single remote API call to some back-end system. If the back-end is down, it will always stop at 90%. The crawling progress bar is fake with canned messages updated with Math.Random() delays. Gives you something to look at, I guess, but seems a little misleading. Might be wrong ...