BUG:

[ElinLiu0]

Pandas version checks

• [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.

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Reproducible Example

No exactly reproduce method

Issue Description

For example i got a DataFrame with null values. Like this

	value
0	1
1	nan
2	2
3	nan
4	nan

So after calling df['value'].ffill(inplace=True),it turns out like:

	value
0	1
1	1
2	2
3	2
4	nan

The last nan hasn't been filled with with 2.

Expected Behavior

It should be filled as		value
0	1
1	1
2	2
3	2
4	2

Installed Versions

INSTALLED VERSIONS

commit : d9cdd2ee5a58015ef6f4d15c7226110c9aab8140 python : 3.11.9.final.0 python-bits : 64 OS : Linux OS-release : 5.15.146.1-microsoft-standard-WSL2 Version : #1 SMP Thu Jan 11 04:09:03 UTC 2024 machine : x86_64 processor : x86_64 byteorder : little LC_ALL : None LANG : C.UTF-8 LOCALE : en_US.UTF-8

pandas : 2.2.2 numpy : 2.0.0 pytz : 2024.1 dateutil : 2.9.0.post0 setuptools : 69.5.1 pip : 24.0 Cython : None pytest : None hypothesis : None sphinx : None blosc : None feather : None xlsxwriter : 3.2.0 lxml.etree : None html5lib : None pymysql : None psycopg2 : None jinja2 : 3.1.4 IPython : 8.26.0 pandas_datareader : None adbc-driver-postgresql: None adbc-driver-sqlite : None bs4 : 4.12.3 bottleneck : None dataframe-api-compat : None fastparquet : None fsspec : None gcsfs : None matplotlib : None numba : 0.60.0 numexpr : None odfpy : None openpyxl : 3.1.5 pandas_gbq : None pyarrow : 16.1.0 pyreadstat : None python-calamine : None pyxlsb : None s3fs : None scipy : None sqlalchemy : None tables : None tabulate : 0.9.0 xarray : None xlrd : None zstandard : None tzdata : 2024.1 qtpy : None pyqt5 : None

[ElinLiu0]

Weried! If i dedicate the fillna function into a component,it works fine. If i run fillna function with beyond code together,it happened again. Why???