the last Pull Requests were unable to fulfill the required checks, because the travis build/check "continuous-integration/travis-ci" was missing. It seems like the following announcement is related to this issue:
"We will no longer deliver GitHub Commit Status API updates for repositories managed by GitHub Apps starting October 4th, 2018." [1].
I will switch the required set of checks from {continuous-integration/travis-ci, Travis-Pull Request} to {Travis-Branch, Travis-Pull Request} which should lead to the same behavior as before. It is probably necessary to retrigger old PR builds (via updating the corresponding branch).
BR,
Kelvin
I realized that the build Travis-Branch is only triggered for "internal" Pull Requests. (Internal PRs are PRs that are created inside the saros repository without forking the repository). For now I will reduce the required checks to Travis-Pull Request (tests the merged version of master and PR branch).
BR,
Kelvin