If a Github repo is renamed, due to the fact that Github supports repository redirects (which doesn't seem possible to disable) Jenkins will create a repository and trigger a build for a repo under the old name and under the new name as well.

Re-scanning the old repo name does not cause it to be removed.

https://developer.github.com/changes/2015-07-21-automatic-redirects-for-renamed-repositories/

This is problematic as it can confuse users and also trigger duplicate builds under the new and old repo names.

Github branch source plugin 2.2.3

Github API plugin 1.86