Github integration broken for a branch with pull request

Cross-posted from DevOps.StackExchange.

I have a branch on Github connected to a pull request. The branch can merge to master only when the tests pass on a Travis build.

Today, the connection between Travis and Github broke down for the branch. I pushed a commit and I see the pull request is waiting for results from Travis:

Github and Travis without link to integration testing results

This appears without the usual link to check details that points to Visiting that page also gives no details on the run. And the Travis interface shows no jobs running.

I tried another commit, and closing and opening the pull request again, with the same result. I tried a new commit on a new branch and Travis integration works with a link to the tests at the bottom right.

I have several commits in that branch that I prefer to keep and merge to master. How can I restore the connection to Travis with the old branch and pull request?

Update: I got the same problem in a more recent pull request, here if anyone wants a closer look.