Add custom content in user-edit.php page

Solved it by using show_user_profile and edit_user_profile instead:

add_action( 'show_user_profile', 'wpse_237901_user_edit_section', 999 );
add_action( 'edit_user_profile', 'wpse_237901_user_edit_section', 999 );

function wpse_237901_user_edit_section() {
    # Code here...
}