BUG: value_counts() is non-reproducible from one run to another
- [X ] I have checked that this issue has not already been reported.

- [X ] 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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**Note**: Please read [this guide](https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports) detailing how to provide the necessary information for us to reproduce your bug.

#### Code Sample, a copy-pastable example

```python
import numpy as np
import pandas as pd

ser = pd.Series(data=['n1', 'n2', 'n0', 'n4', 'n2', 'n1', 'n0', 'n3'], name='ser')

for _ in range(3):
    np.random.seed(42)
    print(ser.value_counts())
    print(ser.value_counts(sort=False))
```

#### Problem description

The output of this file changes from one run to another.  This creates a randomality which cannot be reproduced by np.random.seed(..).

Due to this randomality, the code cannot be made reproducible.

This non-reproducibility happens only from one run to the other; the loop in the code shows that the output is repeated exactly within the same run.

The code shows that the non-reproducibility happens both with value_counts(sort=True) (default value) and value_counts(sort=False).

#### Expected Output

Should be the same from one run to another.

#### Note
This could be related to #32514 or  #32449 but I do not quite understand this.

#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : f2ca0a2665b2d169c97de87b8e778dbed86aea07
python           : 3.6.10.final.0
python-bits      : 64
OS               : Linux
OS-release       : 4.15.0-112-generic
Version          : #113-Ubuntu SMP Thu Jul 9 23:41:39 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8
pandas           : 1.1.1
numpy            : 1.19.1
pytz             : 2020.1
dateutil         : 2.8.1
pip              : 20.2.2
setuptools       : 49.6.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : None
IPython          : None
pandas_datareader: None
bs4              : None
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : None
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.5.2
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : None
xlrd             : None
xlwt             : None
numba            : None


</details>
