Showing "Page not Found" when changing pages and then showing correct page

Hi everyone. I’ve installed the todos app (this one: https://github.com/meteor/todos) and started playing around (I’m learning Meteor). I’m working on the React branch. I removed the .less files to apply a UI library later on.

However, when the Todos app is “naked” (no css styles apply), and I navigate through the lists I see a “Page not found” on the screen for a moment. It is just shown for a second (or even less) and then the correct page is rendered on the screen.

Any idea why this may be happening? Or where to start troubleshooting?

Thanks!