Inconsistent generation with autodata vs automodule

Describe the bug
I am trying to independently reference a set of type definitions in a module. When I use automodule to pull them as a group, the generated docs look about as I would expect. But when I use autodata to reference one indivdually, the generated docs do not have anything other than the header.

To Reproduce
some_module.py

some_var = Union[
  str,
  Dict[str, List[a_typed_dict_from_elsewhere]
]

RST:

.. automodule:: some_module
   :members:
   :undoc-members:
   :show-inheritance:

Output:

some_module.some_var # the header
   alias of {the correct schema} # autodoc 

^^ this is what I expect

RST:

.. autodata:: some_module.some_var
   :annotation:
   :noindex:

Output:

some_module.some_var # the header 

^^ ie, nothing for the alias

<Paste your command-line here which cause the problem>

docs % make html
Running Sphinx v3.2.1
loading pickled environment... done
building [mo]: targets for 0 po files that are out of date
building [html]: targets for 1 source files that are out of date
updating environment: 0 added, 1 changed, 0 removed
reading sources... [100%] dev_guide/getting_started                                         
looking for now-outdated files... none found
pickling environment... done
checking consistency... done
preparing documents... done
writing output... [100%] index                                                              
generating indices...  genindex py-modindexdone
writing additional pages...  searchdone
copying static files... ... done
copying extra files... done
dumping search index in English (code: en)... done
dumping object inventory... done
build succeeded.

Expected behavior
RST:

.. autodata:: some_module.some_var
   :annotation:
   :noindex:

Output:

some_module.some_var # the header 
   alias of {the correct schema} # autodoc 

Environment info

• OS: Mac 10.15.6
• Python version: 3.7.3
• Sphinx version: 3.2.1
• Sphinx extensions: [ 'sphinx.ext.autodoc', 'sphinx.ext.todo', 'sphinxcontrib.napoleon', 'sphinx_autodoc_typehints', 'sphinx_rtd_theme' ]
• Extra tools: None

Additional context
Not 100% sure I am using autodata correctly, so it could be user error.

Reproduce the discrepancy with the some_module.py example and the automodule and autodata RST directives, then run make html. Compare how the two directives render the some_var alias; done means autodata includes the same alias information that automodule shows.