Mark Waite I'm not 100% sure where the issue is, but here is roughly what I have set up:
1. Existing setup running Jenkins 2.32.1, Git Client 2.3.0, Git Plugin 3.0.5, GitHub Plugin 1.26.1, GitHub Branch Source Plugin 2.0.3, and a bunch of other, seemingly unrelated plugins installed (apologies that this isn't a minimal setup to reproduce – I don't have enough existing knowledge of setting up Jenkins for that to be a simple task)
2. Create "New Item" with a GitHub Organization project type
3. Set up the repository sources (private GitHub organization, proper credentials).. Despite what the instructions [here](https://wiki.jenkins-ci.org/display/JENKINS/GitHub+Plugin) say, there is no checkbox for "Build when a change is pushed to GitHub"
4. After Saving the repository source, the organization scans, and the relevant repository also scans. During the scan, branches with a slash in them are picked up just fine. Everything gets triggered the first time.
5. Create a new branch in the repo with a slash (for example, `feature/testing-slashes`), make a whitespace change somewhere, and push a commit
6. Observe that this very first push does trigger a test properly.
7. Make another whitespace change to the new branch, and commit and push that change
8. The branch update does not trigger a test.
I can see in the "All logs" that the GitHub webhook is arriving to Jenkins correctly for the update push, but I don't see any indication in the logs of what happens after the webhook is received.
Another thing that I've observed is that if I navigate to the specific repository and then click on "Scan Repository", then click on "Events", I can see a "CREATED" event in response to the original push of the `feature/test-branch`, which successfully triggers the build, but there is no indication of the UPDATED event for the second push. When I update another branch that doesn't have a slash in it, I do see an UPDATED event that does successfully trigger a build.
Hopefully this helps some. Let me know if there's any other info that I can provide (and preferably how to collect the info, since I'm still fairly new to Jenkins).