I've seen weirder graphs made too, where they curled back on themselves, but the most pressing bug is just that -1|-1 gets reported a few times every now and again.

If you get an undefined number (which you are somehow interpreting as -1), then it would be awesome if it was not written. I notice that around these -1 patches, I see the same bet # reported a few times... so perhaps the page is not loading fully?

Also, another minor improvement might be to block loading unnecessary things. Stuff like the banners and css style sheets take resources and included loading times.

In previous projects, when I have tried to go as lean as possible, I have cut back on things like that. You can easily open a browser window to watch the bot in real time, so do we even need to see the page? This is a pretty big change, so feel free to ignore it.