Because you were "retirement eligible" the FICA tax was collected and paid although the stock had not yet vested.
If you look at the W-2 for that year, your FICA wages should include the not-yet vested stock.
When the stock does vest, if you are no longer receiving a W-2, you will report that as "other Income" which is not subject to FICA tax.
TurboTax never addresses the FICA on RSU because it is done through payroll.