Why isn't the value for a new Boolean field rendered?
This is a Durpal 7 Problem.
It lies about that it will fall back to 0/1 if you don't provide your custom true/false values, when it actually does not fall back.
See
https://www.drupal.org/project/drupal/issues/1750950

In short, in the field-settings, you have to set on-/off- values.
If you don't the default renderer will output an empty string and in the edit forms the field's checkbox or radio-buttons will have no label.