error: Return type of <functionName> incompatible with supertype <ClassName>

I got a code that looks like this:

from typing import NamedTuple, Dict, Optional, List, Any


class Object1(object, metaclass=ABCMeta):
    def __init__(self) -> None:
        pass

    @abstractmethod
    def get_logo(self) -> Optional[str]:
        pass


class Object2(Object1):
    def __init__(self) -> None:
        super().__init__()

    async def get_logo(self) -> Optional[str]:
        return ''


class Object3(Object1):
    def __init__(self) -> None:
        super().__init__()

    async def get_logo(self) -> Optional[str]:
        return None

And the mypy alerts me that:

test.py:19: error: Return type of "get_logo" incompatible with supertype "Object1"
test.py:27: error: Return type of "get_logo" incompatible with supertype "Object1"

But it's look OK to me, because they return the same type...
I run it with: mypy --strict-optional --ignore-missing-imports <file>