Pagination doesn’t work on static front page

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Use
https://codex.wordpress.org/Pagination#static_front_page

And
https://codex.wordpress.org/Creating_a_Static_Front_Page

Other solutions
https://stackoverflow.com/questions/20644991/wordpress-static-page-pagination

the query is diferent on static front pages …
one hack after of your while

<?php if ($the_query->max_num_pages > 1) : // custom pagination  ?>
      <?php
        $orig_query = $wp_query; // fix for pagination to work
        $wp_query = $the_query;

            echo '<div class="both"></div>';
            understrap_pagination(); //your pagination

        $wp_query = $orig_query; // fix for pagination to work
      ?>
    <?php endif; ?>