Removing the form has no effect.
It's very strange. I've made a duplicate of the page. Then essentially removed all elements/widgets (including the signup form), one by one from the page, but the issue still persists even after all widgets are removed. However, when I create a new blank page, using the same page type, the smart search works correctly. Bizarre. My next steps will be to create a blank page type (smart search works at this point), then add in each widget one by one to see where/if the break happens. I'm unable to find any consistency with things going awry.