I am trying to show a dropdown list of all available entries to a custom field, but this is not working - the list is empty.
The options for the field are populated by a lookup that has been put into functions.php that lists all of the available users - I'm not sure if this is what is causing the error?
Alternatively, can I list available users on the site and use that as a filter for a different field?
For example - list all users, but filter the results if the selected name exists in the "wpcf-assigned-to" field?
If you have the field being populated by a list that is dynamically generated then only the values that have been saved to the database will be available in the dropdown. This means you won't be able to pull the values that are not selected by a post.
Alternatively, can I list available users on the site and use that as a filter for a different field?
Listing the available and use those as a filter, unfortunately no this isn't possible unless you are creating a custom field with all the users. If you are populating this list dynamically then you will run into the issue I explained above.