Outer border disappears when hiding outer columns in an s-table__bx table

Describe the bug
Hiding the first or the last column in a table with only horizontal borders (.s-table__bx) via sm:d-none results in the outer border of the table going AWOL on the corresponding side.

To Reproduce
Markup:

<table class="s-table s-table__bx">
      <thead>
          <tr>
              <th scope="col" class="sm:d-none">Something</th>
              <th scope="col">Another</th>
              <th scope="col">Thing</th>
              <th scope="col">Testing</th>
          </tr>
      </thead>
      <tbody>
          <tr>
              <td class="sm:d-none">Hello</td>
              <td>Goodbye</td>
              <td>Maybe</td>
              <td>Wat</td>
          </tr>
      </tbody>
</table>

Toss that into a CodePen or similar, and then resize the window down.

Expected behavior
The outer table border should not disappear.

Screenshots
Before resizing:

After resizing:

Desktop (please complete the following information):

• OS: Windows 10
• Browser: Chrome
• Version 75.0.3770.142

Additional context
The workaround is to add the sm:bl bc-black-3 brw0 classes to the second column of the table (blw0 for the penultimate column).

No source file or test is named. Start by reproducing the provided table markup and responsive sm:d-none behavior, then locate the styles for .s-table__bx and the border utility classes. Done means the corresponding outer border remains visible when the first or last column is hidden at the small breakpoint.