Elective deferrals to a 501(c) plan would be contributions you made to a company retirement plan. Typically, the money would be deducted from your gross pay and contributed to a retirement plan at work. The amounts contributed would not normally be included in your taxable income as reported in box 1 of your W-2 form.
Boxes 3 and 5 of your W-2 form are for reporting your social security and Medicare wages. Those number would be different from your 501(c) plan contributions, so it sounds like something may have went wrong with your W-2 upload. You may have to delete the W-2 entry and download it again, or enter it manually if you continue to experience problems.