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 https://github.com/OWNER/REPO/pull/NUMBER/checks. 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.

Imprint