Hi @elliot and thanks for the quick reply.
Does this mean that it is impossible to order by a true/false ACF field at all, when using WP_Query ?
When the checkbox for that field is unchecked, does ACF save 0 or a NULL into the database ?
Is there a way to define a default value so there are no NULLs in database ?
I’m quite surprised because when you run a query against a table and order by a field, even records with NULL are ordered as expected..