User custom field not display in the backend edit profile
From Joomla! Documentation
User custom field is not displayed and can't be edited in the backend user edit account. Works fine in frontend edit profile.
This pertains only to Joomla! version(s): 3.7.0
What is the cause
Currently the fields that are displayed there are hardcoded.
This is a known problem that is awaiting a fix in a future release: https://github.com/joomla/joomla-cms/issues/13601