Updating Craft to 3.3.19 gives 503 error only for logged-out users Working on an outdated client project and updated craft on staging from 3.0.30.1 to 3.3.19

I'm getting 503 errors (site temporarily unavailable) when trying to visit any page on the site -- but only for logged out users. Once I log in, everything works normally.

I've checked that the DB connection is working correctly. When I performed the updates, I got a dialog from Craft to update my database and performed it so the schemas should be up to date. 

The stack trace shows where the error occurred but I'm stumped as to why it's happening or how to fix it:

From vendor/craftcms/cms/src/web/Controller.php (starts line 157):

        if (!($test &amp; $allowAnonymous)) {
            // If this is a CP request, make sure they have access to the CP
            if ($request-&gt;getIsCpRequest()) {
                $this-&gt;requireLogin();
                $this-&gt;requirePermission('accessCp');
            } else if (Craft::$app-&gt;getUser()-&gt;getIsGuest()) {
                throw new ServiceUnavailableHttpException();
            }


The exception at the bottom of this check is what is thrown and causing the error, but why would a visit to the homepage be detected as a CP request? I'm assuming CP means control panel.

Any ideas?
I've found this question through search. 

I did not perform any update which broke my controllers, but I was unable to access them publicly.

My solution was adding $allowAnonymous = true; to my controller:


class MyController extends \craft\web\Controller
{
    public $allowAnonymous = true;
}