In themable_forms_theme_suggestions_form_element hook there's not check if $variables['element']['#type'] is set.
This cause the error in subject in such cases. For example I had this problem when use "Themable form" module with Message module (https://drupal.org/project/message) in "Message Template" admin page.
This could be the patch:
/**
* Implements hook_theme_suggestions_form_element().
*/
function themable_forms_theme_suggestions_form_element(array $variables) {
if (!isset($variables['element']) || !isset($variables['element']['#type'])) {
return;
}
$suggestions = ['form_element__type__' . $variables['element']['#type']];
if (isset($variables['element']['#form_id'])) {
$suggestions[] = 'form_element__form_id__' . $variables['element']['#form_id'];
$suggestions[] = 'form_element__' . $variables['element']['#form_id'] . '__' . $variables['element']['#type'];
}
return $suggestions;
}
Not all content is available!
It's likely this issue predates Contrib.social: some issue and comment data are missing.
This is a related patch that fixes this issue.
It also contains some extra template suggestions.
Maybe it will help someone as this module appears unmaintained right now.