Order Sprout Forms by field handle returns an error
It seams, that the columns for the form values are not part of the sql, that's why it never will work like this. Maybe it works in upcomming versions of the Sprout Forms plugin. 

As a workaround you can use the SuperSort Plugin. With this plugin it's possible to sort your form entries like you need it.

Step 1 -> Download and Install SuperSort Plugin -> https://topshelfcraft.com/lagniappe/supersort
Step 2 -> Filter your form entries like this:

{% set formEntries = craft.sproutForms.entries.formHandle('contact')%}    
{% set formEntriesSort = formEntries | supersort('sortAs', '{address | lower}') %}

{% for formEntry in formEntriesSort %}
   {{ formEntry.address }}&lt;br&gt;
{% endfor %}


Like this it should work!