BUG: boolean indexing gets different results during multiple runnings

[fengxh0628]

Pandas version checks

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

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

import pandas as pd
d = pd.Series(np.random.randn(1000001).astype(np.float32))
count = (d >= 0).sum()
mean = d.mean()

for i in range(1000):
    c = (d >= 0).sum()
    m = d.mean()
    if c != count:
        print(f'round {i}: not same', c, count, m, mean)

Issue Description

when number of elements larger than 1000000, the bug appears randomly. However, when less than or equal to 1000000, no error was observed.

Expected Behavior

no output

Installed Versions

INSTALLED VERSIONS

commit : 9c8bc3e
python : 3.12.11
python-bits : 64
OS : Windows
OS-release : 11
Version : 10.0.26100
machine : AMD64
processor : AMD64 Family 26 Model 36 Stepping 0, AuthenticAMD
byteorder : little
LC_ALL : None
LANG : None
LOCALE : Chinese (Simplified)_China.936

pandas : 2.3.3
numpy : 2.0.1
pytz : 2025.2
dateutil : 2.9.0.post0
pip : 25.2
Cython : None
sphinx : None
IPython : 9.5.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.13.5
blosc : None
bottleneck : 1.4.2
dataframe-api-compat : None
fastparquet : None
fsspec : None
html5lib : None
hypothesis : None
gcsfs : None
jinja2 : 3.1.6
lxml.etree : None
matplotlib : 3.10.6
numba : None
numexpr : 2.11.0
odfpy : None
openpyxl : None
pandas_gbq : None
psycopg2 : None
pymysql : None
pyarrow : None
pyreadstat : None
pytest : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : 1.16.0
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlsxwriter : None
zstandard : None
tzdata : 2025.2
qtpy : None
pyqt5 : None