Check with your employer's payroll department. Companies can and sometimes do pay dividend equivalent payouts for unvested RSUs. Unlike actual dividends, the dividends on restricted stock will be reported on your W-2 as wages, unless you made a Section 83(b) election. This web reference has a more detailed explanation:
https://www.naspp.com/Blog/May-2019/Dividends-and-Equivalents-Ten-Things-to-Know#:~:text=Since%20div....
Perhaps you paid 2019 tax on a dividend equivalent payout, not on the RSU's themselves.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
