Originally posted here: https://github.com/travis-ci/travis-ci/issues/9917#issuecomment-444254654
The user had been an Outside Collaborator with Read access to a private repository for many weeks, but could not access the Travis CI build logs.
Giving him Write access fixed the issue, but also converting the Outside Collaborator to a Team member to the repo’s organization with Read access fixed the issue.
Unfortunately, GitHub’s documentation on Teams vs. Outside Collaborators on Organization private repositories is somewhat lacking…