Change WordPress user roles and capabilities › Forums › Restrict or Permit access inside WordPress – how to › Enabling a non-Administrator role to view and promote users up to its own role › Reply To: Enabling a non-Administrator role to view and promote users up to its own role
Generally, WordPress roles does not have any built-in (higher/lower) hierarchy.
Were those ‘gold’, ‘silver’, ‘bronze’ added by you or by some membership plugin? If other plugin is involved, it may add own permissions restrictions. To check this assumption, deactivate that plugin and try to promote gold user by gold user again.
Let me know the result of your testing.