Setting a transient from a select option in PHP

I’m trying to set a transient (API reference) from a select option. If I set the transient without redirecting to another page, just set it to redirect to itself, then the transient is set, and when I manually input the URL of the page I should redirect to, it shows up.

However if I directly redirect, it doesn’t register that I’ve set the transient. I’ve come to the conclusion that how I get the variable from the select element is the problem, since it works just like it should if I just put a normal string as the transient, e.g. (on page one):

set_transient('transient_test', "this is a test", 60 * 30);

Here’s how I get the the variable from the select element (on page one):

if (isset($_POST['industry']) == true) {
      $selectOption = $_POST['industry'];
      set_transient('industry_transient', $selectOption, 60 * 30);
}

I test if the transient is the variable I want it to be (on page one):

if (isset($_POST['industry']) == true) {
                                $selectOption = $_POST['industry'];
                                set_transient('industry_transient', $selectOption, 60 * 30);
                                $selected = get_transient('industry_transient');
                                echo $selected;
                        }

Here’s how I get the transient (on page 2):

$transient = get_transient('industry_transient');

I test it like this, and I always get a “no transient” when I redirect immediately (on page 2):

if (false === ($value = get_transient('industry_transient'))) {
      echo 'no transient';
}

if (true === ($value = get_transient('industry_transient'))) {
      echo 'yes transient';
}

Here’s my form (page one):

<form method="post" action="http://localhost:8888/wordpress/candidates/industry">
                        <select name="industry">
                                <option disabled selected> -- Select an industry -- </option>
                                        <option value="Example">there are a lot of options...</option>
                        </select>
                        <input type="submit" value="Submit">
                </form>

I tried setting the transient within the form tag, however, it made no difference.