When a branch is created from an existing commit in a Git repository in Bitbucket, the webhook fires notifying Jenkins of the push, but the Jenkins webhook log decides "No changes" and does not trigger a build. However, we now have a branch in the repository with no matching builds in the jobs API, which breaks our automation pipeline.

It is understandable not to run a build when there are no changes, but if it's not going to build, it should at least update the existing build of that commit to associate it with the new branch, so that the jobs API responds correctly indicating that the existing build for that commit is associated with the new branch for that commit.

Note that at least two other people have encountered the same problem judging from this unanswered post: https://stackoverflow.com/q/37864608/