How to insert form in DataBase
Removing the #submit key fixed the submission issue for me:

$form['save'] = array(
    '#type' =&gt; 'submit',
    '#input' =&gt; TRUE,
    '#value' =&gt; 'save',
    //'#submit' =&gt; array('buildForm')
);


DB insert works correctly.

If you do return $form; in the buildForm() method, the radios form element is rendered correctly. Looks like your theme might be causing the issue.