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.
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