bokeh app only sometimes updates in response to slider change

I am using bokeh to map speeds on road links in San Francisco. So far, I’m impressed with the package, so nice work. Starting from the SlidersApp example, I set this up with a slider for the hour of the day, and to change the color of the links based on the speed in that hour. I am plotting about 30,000 multi_lines to do this.

My problem is this: in response to changing the slider, my plot sometimes, but does not always update. In addition, it sometimes updates out of order. The screenshot below shows a case where I moved the slider from hour 5 to hour 17. You can see in the open command window with the server output that it is executing my update_data() method because it prints out “updating to hour XX”. However, you can see that the sequence of updates is: 5-6-7-8-14-15-17-16. If you look at the browser, you see that my slider is set to 17, but based on the title, the plot is rendering for hour 16. In other cases, I can move the slider bar and the plot does not change.

I would add that this works pretty smoothly for plots having less than about 10,000 multi_lines, but struggles for the larger plots.

A related issue is that the hover tool works when the plot first loads, but not after changing the slider bar.

For reference, my code is available here:

Thanks for any help you can provide.