Inconsistent type references when using autodoc

Describe the bug

I have the following python code:

"""My Implementation"""
from typing import Collection

from sphinx_autodoc.api import MyInterfaceClass


class MyClass:  # pylint: disable=too-few-public-methods
    """This is my class and its doc
    
    This is a reference to :class:`~sphinx_autodoc.api.MyInterfaceClass`
    
    """

    delegate: MyInterfaceClass
    """Some delegate"""

    external: Collection
    """Some external reference"""

    def get_delegate(self) -> MyInterfaceClass:
        """Gets the delegate

        Returns:
            the delegate
        """
        return self.delegate

    def get_external(self) -> Collection:
        """Gets the delegate

        Returns:
            the delegate
        """
        return self.external


VARIABLE: MyClass = MyClass()
"""This is my variable and its doc"""

When producing a Sphinx documentation with the following config:

extensions = [
    'sphinx.ext.intersphinx',
    'sphinx.ext.napoleon',
    'sphinx_autodoc_typehints',
    'sphinx.ext.autodoc'
]

# Some config
intersphinx_mapping = {'python': ('https://docs.python.org/3', None)}

I see the following unexpected behaviour:

• the global property VARIABLE does not appear in the documentation at all
• in the documentation of MyClass I find:
  • the reference to MyInterfaceClass in the docstring of the class correctly links to the documentation of MyInterfaceClass
  • there is no link at all on the documentation of the type of the instance propery delegate (https://github.com/Carsten-Leue/sphinx-autodoc/blob/master/build/docs/sphinx_autodoc.html#L189)
  • the styling of the the type of the instance propery delegate visually does not look like the styling for the same type on the return value of get_delegate
  • there is no link at all on the documentation of the type of the instance propery external (https://github.com/Carsten-Leue/sphinx-autodoc/blob/master/build/docs/sphinx_autodoc.html#L195)
  • the documentation of the function get_delegate() shows the correct return type but there is no link on that type to the documentation (despite the fact that there is a link to the same class in the class level docstring) (https://github.com/Carsten-Leue/sphinx-autodoc/blob/master/build/docs/sphinx_autodoc.html#L205)
  • the documentation of the function get_external() shows the correct return type and there exists a link to the documentation of the return value (but the same return value is not linked for the equivalent instance property)

To Reproduce

I have created a small test repo to illustrate and reproduce the issue:

• clone https://github.com/Carsten-Leue/sphinx-autodoc
• install tox
• run tox -e doc

The result of this step is also checked in at https://github.com/Carsten-Leue/sphinx-autodoc/tree/master/build/docs

Expected behavior

• Linking to types in my own project (across submodules) works consistently, everywhere where a type gets referenced, i.e. in types for arguments, return values, variables and refences in doc strings

Your project

https://github.com/Carsten-Leue/sphinx-autodoc

Environment info

• OS: Windoes 10
• Python version: Python 3.8.4 (tags/v3.8.4:dfa645a, Jul 13 2020, 16:46:45) [MSC v.1924 64 bit (AMD64)] on win32
• Sphinx version: 3.1.2
• Sphinx extensions: ['sphinx.ext.intersphinx',
  'sphinx.ext.napoleon',
  'sphinx_autodoc_typehints',
  'sphinx.ext.autodoc']

Clone the linked reproduction repository and run tox -e doc; inspect the generated pages under build/docs and compare links for class docstrings, properties, return values, and the global variable. Trace the autodoc and sphinx_autodoc_typehints handling for these references, then verify that equivalent project and external type references render consistently.