Troubleshooting Git Polling may be cumbersome. Found out recently a case where Polling would report changes without telling us why:

Using strategy: Default
[poll] Last Built Revision: Revision xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (refs/remotes/origin/<branch>)
no polling baseline in <workspaceLocation> on <sampleNodeName>
Done. Took 6 ms
Changes found

Looking at the code, there might be cases where the workspace exists but the workingDirectory doesn't: https://github.com/jenkinsci/git-plugin/blob/git-4.0.0-rc/src/main/java/hudson/plugins/git/GitSCM.java#L773. It would be ideal for diagnosability that before returning any PollingResult, a relevant log be printed.