The NUA only becomes taxable as LTCG when the shares are sold. When they are sold they will be reported on Form 1099-B as non-covered shares where you'll need to provide the cost basis (or at least confirm that the cost basis shown on the Form 1099-B is correct.
Also keep in mind that any capital gains subsequent to the distribution from the ESOP account are short-term until the shares have been outside the ESOP account for a year or more.
Apparently there was a small amount of cash distributed with the ESOP shares since without cash being distributed there can be no tax withholding. There's a good changes that cash was pre-tax money that was included in the taxable amount in box 2a. If so, that would make the total cost basis of the ESOP shares the amount in box 2a minus the amount in box 4.
