I am trying out the ACF 5.8.13 (Free) version on WordPress 5.4.2. This is a local machine install on Ubuntu + MySQL 8.0.21.
The problem is that I am unable to add more than 10 (ten) fields to a field group. When I add an 11th field and hit the UPDATE button, the message alert on the top says that the fields have been saved. But, when the field-group refreshes, it only has the first 10 fields.
What I have tried:
1. Create a fresh field group that is not bound to any post type (post type query is blank).
2. Created a field-group, added 10 fields, exported it to JSON (using the Custom Fields > Tools > Export Field Groups), added the 11th field to it using a text editor. Deleted the original field group from WP-ADMIN, cleared it from Trash as well. Imported the modified JSON using the Custom Fields > Tools > Import Field Groups.
I also attempted to trace through the code to figure out what was going on, but with so many filters and nested logic, it was kind of hard to get anywhere. However, I did confirm that both the acf_update_field() and acf_update_field_group() functions were doing their job. In both cases, the fields were reported as committed to the database.
Interestingly, I can see that in the WP_POSTS table in the database, these fields ARE PRESENT. But they do not show up on any UI !
I have confirmed that if I delete one or more fields from the group and add, I can continue to add to it. But anything after 10 fields fails to show up. They don’t appear in the exported JSON or in the “Generate PHP” code either.