Frontend Form - Checkboxes cannot "all" be unchecked I have a frontend entry form with some checkboxes that is not behaving correctly.

If you uncheck all options and save, nothing changes (this is bad). However if you uncheck one item and check another item it saves correctly.

Additionally in the Craft CP if you uncheck all items it saves correctly so it clearly works there. 

relevant template code:

{% for volunteer in craft.entries.section('careers').search('positionType:volunteerPosition') %}
  &lt;label class="d-block"&gt; 
        &lt;input type="checkbox" class="form-check-input" name="fields[volunteerPositions][]" class="form-check-input" value="{{volunteer.id}}" {% if volunteer.id in selectedEntries %}checked{% endif %}&gt;&amp;nbsp;&amp;nbsp;{{volunteer.title}}  (created by {{volunteer.author }}) 
      &lt;/label&gt; 
{% endfor %}


Please advise.
Your code is correct but you need to add another line near the top:

 &lt;input type="hidden" name="fields[volunteerPositions]" value=""&gt;


From the documentation:


  If you are including a Checkboxes field on a front-end entry from, make sure to include a hidden input before the checkboxes, so that an empty value is submitted if no checkboxes are checked.