I just found out what the problem was. All properties that had never been edited before the addition of the “is_featured” field had no value in that field (not even “false” value) that’s why they weren’t being displayed. To fix it I had tu run a process that added the “false” value to all properties that had no value set.
If you ask me, I think WordPress should still display at the end all posts that don’t have a value set in the custom field, but it looks like it just does not work that way.
