So I came back to it this morning and it’s working fine??? I was purging caches yesterday while I was working on it just to make sure it wasn’t some weird wordpress caching issue, and yet…
I don’t even know what to tell you. I’m a little thrown. The display thumbnail check box is working fine today. I switched it on and off a few times just to make sure.
If I try to use the shortcode it still doesn’t work, but the featured images are being set correctly, at least.
I’m sorry to have bothered you, I guess.