It took me some time to figure out what was the problem. The Appearance > Elements display was broken. On my dev website, it displayed the custom taxonomies list, that were supposed to be in the select list under Display Rules, in the middle of the page…
I have custom post types with “has_archive” => false. In this case, $type[‘label’] (line 1143 in class-metabox.php) returns an empty value, breaking the construction of the select list.
Turning has_archive back to true fixed the problem.
I thought I’ll let you know ;).
Best regards,
P