System information

• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): windows
• Modin version (modin.__version__): latest
• Python version: 3.8
• Code we can use to reproduce:

import modin.pandas as pd

df = pd.read_csv("some.csv", index_col=[0,1,2])
df.reset_index().groupby(df.columns[:1]).count()  # error

Describe the problem

This only happens in a very corner case: when groupby by parameter contains 2 or more columns added from the reset_index call.