Ok all, I think I figured out the problem…well, problemS. First, credit to @WebElaine, for putting me on the right track with the unregister_post_type() function.
I unregistered ALL of my post types, then went through and made sure everything was singular with no trailing S. After unregistering everything (and commenting out any code that would register anything in the interim) I then went and refreshed my permalinks. After that, I removed the unregistering function, and uncommented my previous code and allowed things to register. This seemed to fix the issue and now the template is being read correctly.
Thank you all for the suggestions and help. I’m a newly minted Jr Dev and am always blown away by the supportive dev community. Hope anyone who lands here with the same frustration finds this helpful!