After hours on the phone with TurboTax, we found the answer. If your income is less than the threshold, the IRS does not want you to use Form 8959 to get excess Medicare withholding back. They instruct you to work it out with your employer, or file a claim with them. See this answer for details:
https://ttlc.intuit.com/questions/4677534-can-i-get-a-refund-for-excess-medicare-tax-withheld
