Test passes in headed mode but fails on headless

This test passes in headed mode but not in headless mode. Why is this?

it.only('should sequence numbers on the second page', async ({ page }) => {
            await nextPage.click();
            await page.waitForTimeout(500);
            const el1 = page.getByRole('cell').filter({ hasText: '14' }); // using 14 because 13 is also used in dob
            const el2 = page.getByRole('cell').filter({ hasText: '25' }); // last row on page
                                                     
            expect(el1).toBeVisible();               
            expect(el2).toBeVisible();               
          });