When trying to activate an offshoot from an interface inheriting from the ACS::OffShoot interface, we end up with the container claiming it's not an OffShoot. An example:

2020-11-30T15:21:24.293 aragornContainer activateOffShoot - Not an OffShoot '<CALLBACKS_IMPL_MODULE.MyCallbackImpl.MyCallbackImpl object at 0x7efc80466470>'

This is because the check is being done at Python level:

elif not isinstance(os_corba_ref, OffShoot):

    ...

The problem is that the servant implementations don't inherit from all the definitions in CORBA:

Class: <class 'CALLBACKS_IMPL_MODULE.MyCallbackImpl.MyCallbackImpl'>

Bases: (<class 'AsyncModule__POA.MyCallback'>,)

So it would never have ACS__POA.OffShoot as base. The solution is to use CORBA's narrow instead, which correctly handled the IDL inheritance between interfaces:

elif os_corba_ref._this()._narrow(OffShoot) is None:

    ...