We use Jenkins' Git plugin to run our tests, but we prefer not to clean workspace before each build and reuse the code in the workspace instead. This makes testing much faster. Unfortunately, sometimes the Git information on the workspace gets corrupted and git fetch no longer works (unrelated to the Git plugin). This means that future build on that workspace will fail unless the workspace is cleaned.
It would be very good if Jenkins' Git plugin had the ability to clear the workspace before doing a retry.