We got it fixed. Thanks Trevor! Here was the resolution:
I am using the ACF taxonomy field on the edit screen to provide a better user interface for adding taxonomies (I wanted the site admin to be able to search and pick from a list of existing values instead of typing them, and also restrict them to one choice).
It turns out there is a miscommunication between S&F and ACF. S&F had a hard time reading the ACF value for those taxonomy terms as they were output in the results table. You’ll notice I was using the ACF field to try to output the taxonomy term into the search results. That’s where the breakdown occurred. Turns out that was unnecessary because I had also linked the ACF taxonomy field to the CPT custom taxonomy.
The resolution here was to output the taxonomy term using a WordPress function, get_the_terms(), instead of the ACF function. This is what I changed from the code in my first post:
<div class="inv_make"><?php echo get_the_terms(get_the_ID(), 'vehicle_make')[0]->name; ?></div>
<div class="inv_model"><?php echo get_the_terms(get_the_ID(), 'vehicle_model')[0]->name; ?></div>
I will note here that I’m only allowing one term per taxonomy which is why I don’t have this in a loop (which I would need if there was more than one term per taxonomy).