Two things pop up in my mind, first have you ensured that the module defining the custom_field_name is properly installed and that its dependencies are correctly set up? If your custom field is in a module that extends or depends on other modules, ensure those are loaded first.

Secondly, check the Python model where custom_field_name is defined. Ensure that the field is correctly declared and follows the correct syntax. For One2many and Many2many fields, ensure the relation and inverse names are correctly specified.