API returning duplicated, contradicting values

Describe the bug upon specific API calls on stock time series data, the returned data has non-unique timestamps with

To Reproduce Steps to reproduce the behavior:

call the API for monthly SPX data and look at the result execute the following code:

from twelvedata import TDClient
import pandas as pd

# Initialize client - apikey parameter is requiered
td = TDClient(apikey=api_key)

interval = '1month'
symbol = 'SPX'

ts = td.time_series(
    symbol=symbol,
    interval=interval,
    outputsize=5000,
    timezone="UTC",
    exchange= 'NYSE',
    start_date= '2000-01-01 00:00:00',
#     end_date = end_date,
    order= 'asc',
)

# Returns pandas.DataFrame
result=ts.as_pandas()
print(result[result.index.duplicated(keep=False)])

result of print:


                  open        high         low       close       volume
datetime                                                               
2006-01-01  1248.29004  1294.90002  1245.73999  1280.07996            0
2006-01-01  1248.29004  1294.90002  1245.73999  1282.45996            0
2006-02-01  1280.07996  1297.56995  1253.60999  1280.66003            0
2006-02-01  1282.45996  1297.56995  1253.60999  1291.23999            0
2006-03-01  1280.66003  1310.88000  1268.42004  1294.82996            0
...                ...         ...         ...         ...          ...
2020-01-01  3244.66992  3337.77002  3214.63989  3225.52002            0
2020-02-01  3235.65991  3393.52002  2855.84009  2954.21997            0
2020-02-01  3235.65991  3393.52002  2855.84009  2954.21997            0
2020-03-01  2982.50000  3090.22998  2944.89990  3090.22998            0
2020-03-01  2974.28003  3136.71997  2191.86011  2578.52002  59996936715

we can see many monthly dates with two entries instead of one, and some pairs even have contradicting values.

Expected behavior the print statement should return an empty dataframe

Screenshots If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

OS: Win10
Browser Firefox
Version 84.0.2

Additional context Add any other context about the problem here.

twelvedata / twelvedata-python

API returning duplicated, contradicting values #29