Another issue has taken precedence: the background caching doesn’t work, wp_remote_get(), and it needs to work. It doesn’t work on my local server, nor on the production server. I threw a rudimentary wp_remote_get-based script (not related to the search filter plugin or operations) just to test wp_remote_get’s functionality, and it appeared to be retrieving data fine.
I must get the background processing to function, as I tried foreground processing, but after 20 hours of miserably wheeling around with that, it only reached ~44k posts of the 67.5k posts in the system, then made a change or two and it started over at 0, so foreground processing is completely out of the option as posts are constantly being added.