Low Search category filter not returning results

Question

This is a follow-up question related to another thread, Combine multiple categories into one select option.

I have a Low Search form that works like a quiz, narrowing down entries within a channel through the category filter. I'm seeing an issue whereby the search results page defaults to the same result no matter which options I choose.

I've confirmed that the proper categories are applied to the channel entries. It doesn't "remember" the categories searched on and just displays the same result over and over.

At first I thought this might be a caching issue but if you visit the page linked below and then click the submit button without selecting any options you'll see results return for the "1 Bedroom" category.

Question: Why are the category filters not being applied to the search query?

I am on EE 2.8.1, Low Search 3.5.2 and am also using Stash, Switchee, Structure and Freebie. The query parameter is set to {freebie_3} for the form tag and the results tag. I'm guessing there is some caching issue with the template but since it's working locally I'm at a loss as to what could be different across the environments.

Here's the link to see the form in action:

http://staging.l45living.com/floor-plans

Here's the form code for reference (with some code removed):

{exp:low_search:form
  form_id="submit-quiz"
  query="{freebie_3}"
  result_page="/floor-plans/search"
}

      <div class="row">
        <div class="small-12 medium-5 columns">
          <label class="inline" for="bedrooms">Number of bedrooms?</label>
        </div>
        <div class="small-12 medium-7 columns">
          <select name="category[]">
            <option value="">Show me all the options!</option>
            {exp:channel:categories
              category_group="1"
              show="not 4"
              style="linear"
            }
              <option value="{category_id}"{if low_search_category ~ '/\b'.category_id.'\b/'} selected{/if}>
                {category_name}
              </option>
            {/exp:channel:categories}
          </select>
        </div>
      </div>

      <div class="row">
        <div class="small-12 medium-5 columns">
          <label class="inline" for="floor">What floor do you like?</label>
        </div>
        <div class="small-12 medium-7 columns">
          <select name="category[]">
            <option value="">Show me all the options!</option>
            {exp:channel:categories
              category_group="2"
              show="28|29|30"
              style="linear"
            }
              <option value="{category_id}"{if low_search_category ~ '/\b'.category_id.'\b/'} selected{/if}>
                {category_name}
              </option>
            {/exp:channel:categories}
          </select>
        </div>
      </div>

      <div class="row">
        <div class="small-12 medium-5 columns">
          <label class="inline" for="view">What would you like your view to include?</label>
        </div>
        <div class="small-12 medium-7 columns">
          <select name="category[]">
            <option value="">Show me all the options!</option>
            {exp:channel:categories
              category_group="3"
              style="linear"
            }
              <option value="{category_id}"{if low_search_category ~ '/\b'.category_id.'\b/'} selected{/if}>
                {category_name}
              </option>
            {/exp:channel:categories}
          </select>
        </div>
      </div>

      <div class="row">
        <div class="small-12 medium-5 columns">
          <label class="inline" for="pets">Are you bringing a pet?</label>
        </div>
        <div class="small-12 medium-7 columns">
          <select name="category[]">
            {exp:channel:categories
              category_group="5"
              style="linear"
            }
              <option value="{category_id}"{if low_search_category ~ '/\b'.category_id.'\b/'} selected{/if}>
                {category_name}
              </option>
            {/exp:channel:categories}
          </select>
        </div>
      </div>

      <div class="row">
        <div class="small-12 medium-5 columns">
          <label class="inline" for="lifestyle">What's your lifestyle?</label>
        </div>
        <div class="small-12 medium-7 columns">
          <select name="category[]">
            <option value="">No preference. I go with the flow</option>
            {exp:channel:categories
              category_group="4"
              style="linear"
            }
              <option value="{category_id}"{if low_search_category ~ '/\b'.category_id.'\b/'} selected{/if}>
                {category_name}
              </option>
            {/exp:channel:categories}
          </select>
        </div>
      </div>

      <div class="row">
        <div class="small-8 small-centered columns">
          <button id="btn-submit-quiz" type="submit" class="submit">Find my perfect apartment</button>
        </div>
      </div>
    {/exp:low_search:form}

Here's the results code for reference (with some markup removed):

{exp:low_search:results
  channel="units"
  orderby="title"
  query="{freebie_3}"
  require_all="category"
  sort="asc"
}
  ....    
{/exp:low_search:results}