My guess is the file.startswith(basedir) in the getdocloc() method is getting tricked by non-canonical paths (e.g. lowercase vs uppercase C: drive?). Would it help to use something like os.path.normcase(), or maybe os.path.commonpath(), pathlib.PurePath.parts or PurePath.relative_to()?

file = inspect.getabsfile(object)
...
basedir = os.path.normcase(basedir)
if (...
     (file.startswith(basedir) and ...

Also, in the new get_pydoc_link() function, is that os.path.join() call meant to be there?

basedir = os.path.join(dirname(dirname(__file__)))