I have created an extra field in res.partner in Odoo 12 CE. I have made 2 custom modules which can inherit this field [registration = fields.Char(related='partner_id.registration')]. This works fine in the first module. However, in the second module, even though I can see the field has been created (in the list of fields from the Model in the Technical Menu), one I try adding the field to the views, it gives me the following error: 

File "/home/ubuntu/odoo/odoo/fields.py", line 527, in _setup_related_full
    field = target._fields[name]
KeyError: 'registration'

Full error is below:

Traceback (most recent call last): 
File "/home/ubuntu/odoo/odoo/http.py", line 656, in _handle_exception 
return super(JsonRequest, self)._handle_exception(exception) 
File "/home/ubuntu/odoo/odoo/http.py", line 314, in _handle_exception 
raise pycompat.reraise(type(exception), exception, sys.exc_info()[2]) 
File "/home/ubuntu/odoo/odoo/tools/pycompat.py", line 87, in reraise 
raise value 
File "/home/ubuntu/odoo/odoo/http.py", line 698, in dispatch 
result = self._call_function(**self.params) 
File "/home/ubuntu/odoo/odoo/http.py", line 346, in _call_function 
return checked_call(self.db, *args, **kwargs) 
File "/home/ubuntu/odoo/odoo/service/model.py", line 97, in wrapper 
return f(dbname, *args, **kwargs) 
File "/home/ubuntu/odoo/odoo/http.py", line 339, in checked_call 
result = self.endpoint(*a, **kw) 
File "/home/ubuntu/odoo/odoo/http.py", line 941, in __call__ 
return self.method(*args, **kw) 
File "/home/ubuntu/odoo/odoo/http.py", line 519, in response_wrap 
response = f(*args, **kw) 
File "/home/ubuntu/odoo/addons/web/controllers/main.py", line 966, in call_button 
action = self._call_kw(model, method, args, {}) 
File "/home/ubuntu/odoo/addons/web/controllers/main.py", line 954, in _call_kw 
return call_kw(request.env[model], method, args, kwargs) 
File "/home/ubuntu/odoo/odoo/api.py", line 749, in call_kw 
return _call_kw_multi(method, model, args, kwargs) 
File "/home/ubuntu/odoo/odoo/api.py", line 736, in _call_kw_multi 
result = method(recs, *args, **kwargs) 
File "<decorator-gen-67>", line 2, in button_immediate_upgrade 
File "/home/ubuntu/odoo/odoo/addons/base/models/ir_module.py", line 74, in check_and_log 
return method(self, *args, **kwargs) 
File "/home/ubuntu/odoo/odoo/addons/base/models/ir_module.py", line 622, in button_immediate_upgrade 
return self._button_immediate_function(type(self).button_upgrade) 
File "/home/ubuntu/odoo/odoo/addons/base/models/ir_module.py", line 561, in _button_immediate_function 
modules.registry.Registry.new(self._cr.dbname, update_module=True) 
File "/home/ubuntu/odoo/odoo/modules/registry.py", line 86, in new 
odoo.modules.load_modules(registry._db, force_demo, status, update_module) 
File "/home/ubuntu/odoo/odoo/modules/loading.py", line 417, in load_modules 
force, status, report, loaded_modules, update_module, models_to_check) 
File "/home/ubuntu/odoo/odoo/modules/loading.py", line 313, in load_marked_modules 
perform_checks=perform_checks, models_to_check=models_to_check 
File "/home/ubuntu/odoo/odoo/modules/loading.py", line 194, in load_module_graph 
registry.setup_models(cr) 
File "/home/ubuntu/odoo/odoo/modules/registry.py", line 267, in setup_models 
model._setup_fields() 
File "/home/ubuntu/odoo/odoo/models.py", line 2609, in _setup_fields 
field.setup_full(self) 
File "/home/ubuntu/odoo/odoo/fields.py", line 484, in setup_full 
self._setup_related_full(model) 
File "/home/ubuntu/odoo/odoo/fields.py", line 527, in _setup_related_full 
field = target._fields[name] 
KeyError: 'registration'