BUG: Freq argument lost using pd.infer_freq

[rwijtvliet]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

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Code Sample, a copy-pastable example

import pandas as pd

# reference, works: 2 normal days.
i0 = pd.date_range('2020-09-24', '2020-09-26', freq='H', closed='left', tz='Europe/Berlin')
pd.infer_freq(i0)  # 'H'   (i0.freq == '<Hour>')

# problem, does not work: summertime to wintertime changeover.
i1 = pd.date_range('2020-10-24', '2020-10-26', freq='H', closed='left', tz='Europe/Berlin')
pd.infer_freq(i1)  # '' <-- !!!!!    (even though i1.freq == '<Hour>')

# for completeness, works: wintertime to summertime changeover
i2 = pd.date_range('2020-03-28', '2020-03-30', freq='H', closed='left', tz='Europe/Berlin')
pd.infer_freq(i2)  # 'H'     (i2.freq == '<Hour>')

Problem description

Even though i1 has the frequency attribute correctly set, pd.infer_freq(i1) returns an empty string.

Expected Output

'H', just like when using i0 or i2.

Output of pd.show_versions()

INSTALLED VERSIONS

commit : db08276
python : 3.8.5.final.0
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.18362
machine : AMD64
processor : Intel64 Family 6 Model 158 Stepping 10, GenuineIntel
byteorder : little
LC_ALL : None
LANG : en
LOCALE : de_DE.cp1252

pandas : 1.1.3
numpy : 1.19.2
pytz : 2020.4
dateutil : 2.8.1
pip : 20.3
setuptools : 50.3.2.post20201202
Cython : None
pytest : 6.1.2
hypothesis : None
sphinx : 3.2.1
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : 1.0.1
pymysql : None
psycopg2 : None
jinja2 : 2.11.2
IPython : 7.19.0
pandas_datareader: None
bs4 : 4.9.1
bottleneck : None
fsspec : None
fastparquet : None
gcsfs : None
matplotlib : 3.3.2
numexpr : None
odfpy : None
openpyxl : 3.0.5
pandas_gbq : None
pyarrow : None
pytables : None
pyxlsb : None
s3fs : None
scipy : 1.5.2
sqlalchemy : 1.3.20
tables : None
tabulate : None
xarray : None
xlrd : 1.2.0
xlwt : None
numba : None

[lithomas1]

@rwijtvliet I cannot reproduce this on master anymore, it looks like this was fixed by #39644. (xref #39556). If you also cannot reproduce this on master, please close the issue. Thanks!

[mroeschke]

Closing as fixed and working on master.