# Buggy code
def _map_reduce(self, axis, map_func, reduce_func=None, preserve_index=True):
    """
    Apply function that will reduce the data to a Pandas Series.

    Parameters
    ----------
        axis : 0 or 1
            0 for columns and 1 for rows.
        map_func : callable
            Callable function to map the dataframe.
        reduce_func : callable
            Callable function to reduce the dataframe.
            If none, then apply map_func twice. Default is None.
        preserve_index : boolean
            The flag to preserve index for default behavior
            map and reduce operations. Default is True.

    Returns
    -------
    BasePandasFrame
        A new dataframe.
    """
    map_func = self._build_mapreduce_func(axis, map_func)
    if reduce_func is None:
        reduce_func = map_func
    else:
        reduce_func = self._build_mapreduce_func(axis, reduce_func)

    map_parts = self._frame_mgr_cls.lazy_map_partitions(self._partitions, map_func)
    reduce_parts = self._frame_mgr_cls.map_axis_partitions(axis, map_parts, reduce_func)
    if preserve_index:
        return self._compute_map_reduce_metadata(axis, reduce_parts)
    else:
        if axis == 0:
            new_index = ["__reduced__"]
            new_columns = self._frame_mgr_cls.get_indices(
                1, reduce_parts, lambda df: df.columns
            )
        else:
            new_index = self._frame_mgr_cls.get_indices(
                0, reduce_parts, lambda df: df.index
            )
            new_columns = ["__reduced__"]
        return self.__constructor__(
            reduce_parts, new_index, new_columns, validate_axes="reduced"
        )


# Traceback (Exception)
Traceback (most recent call last):
File "test.py", line 15, in <module>
print(f"modin:\n{modin_df.sum(min_count=1)}")
File "modin\pandas\base.py", line 3512, in __str__
return repr(self)
File "modin\pandas\series.py", line 307, in __repr__
temp_df = self._build_repr_df(num_rows, num_cols)
File "modin\pandas\base.py", line 108, in _build_repr_df
return self.iloc[indexer]._query_compiler.to_pandas()
File "modin\backends\pandas\query_compiler.py", line 191, in to_pandas
return self._modin_frame.to_pandas()
File "modin\engines\base\frame\data.py", line 1801, in to_pandas
"Internal and external indices do not match.",
File "modin\error_message.py", line 54, in catch_bugs_and_request_email
" caused this error.\n{}".format(extra_log)
Exception: Internal Error. Please email bug_reports@modin.org with the traceback and command that caused this error.
Internal and external indices do not match.

# Fixed code
def _map_reduce(self, axis, map_func, reduce_func=None, preserve_index=True):
    """
    Apply function that will reduce the data to a Pandas Series.

    Parameters
    ----------
        axis : 0 or 1
            0 for columns and 1 for rows.
        map_func : callable
            Callable function to map the dataframe.
        reduce_func : callable
            Callable function to reduce the dataframe.
            If none, then apply map_func twice. Default is None.
        preserve_index : boolean
            The flag to preserve index for default behavior
            map and reduce operations. Default is True.

    Returns
    -------
    BasePandasFrame
        A new dataframe.
    """
    map_func = self._build_mapreduce_func(axis, map_func)
    if reduce_func is None:
        reduce_func = map_func
    else:
        reduce_func = self._build_mapreduce_func(axis, reduce_func)

    map_parts = self._frame_mgr_cls.lazy_map_partitions(self._partitions, map_func)
    reduce_parts = self._frame_mgr_cls.map_axis_partitions(axis, map_parts, reduce_func)
    return self._compute_map_reduce_metadata(
        axis, reduce_parts, preserve_index=preserve_index
    )