I’m still not sure what was going on, but updating to the latest version of ACF seems to have fixed it.
Hi, John,
Thanks for the advice!
Unfortunately, none of this helps. I have tried using my code on a fresh WordPress site, with no plugins installed, using the TwentyFifteen theme, and I get the same results, so it’s not a plugin conflict or a priority issue (and I have also tried changing the priority). Clearing the cache seemed promising, but didn’t change anything.
Using define( 'ACF_LITE', true );
to hide the UI works, but doesn’t solve the problem of my fields not being registered.