Traditionally, Travis-ci provides 2 platforms: travis-ci.com - for private/paid repos and travis-ci.org - for free repos. But according to this announcement, all projects from .org will move to .com eventually.

The problem is that when setting travis_button=True, the badge displays the build status of the repo from travis-ci.org, which might not be the case for all the users. For someone having the repo activated on travis-ci.com, the badge will not show the proper build status.

For instance, in my case, the build was passing, but the badge showed unknown - since my repo is activated on travis-ci.com and not on travis-ci.org.