Out-File not reporting error on failure to write to UNC network path when stream is being repeatedly opened and closed.

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues.
• Refer to the FAQ.
• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

I am trying to extract a representative sample of a 200MB csv file by writing the header and every 500th row to a new file for testers to use. I relied on out-file -append to add each row matching the modulus condition to the destination file on network share, but what I found is that I had slightly fewer rows in the sample file than expected. Repeated runs produced slightly different numbers of rows in the destination file (expected 2014, actual ranged between 1992-2011). I did not get an terminating error.

The behaviour does NOT occur if I use a location on my local hard drive for the destination file.

$destfile = "\\UNCSHARE\Folder\Export_Sample_$(get-date -Format "yyyyMMdd_HHmmss").txt"

$Original = get-content "\\UNCSHARE\Folder\200MB_Export_20231208_1545.txt"

[int64]$ln = 0
[int64]$SampleCount = 0

foreach ($line in $Original) {
    $ln++
    if ($ln -eq 1 -or $ln % 500 -eq 0) {
        $line | Out-File -FilePath $destfile -Append -ErrorAction Stop
        $SampleCount++
    }
}
write-host $SampleCount

(get-content $destfile).count 

I tried a suggested alternative of switching to the native API call:

#$line | Out-File -FilePath $destfile -Append -ErrorAction Stop -Encoding utf8
[System.IO.File]::AppendAllText($destfile, "$line`n")

That still doesn't produce a terminating error in Powershell 7.4.2, but does in Windows Powershell 5.1

Exception calling "AppendAllText" with "2" argument(s): "The process cannot access the file 
'\\UNCSHARE\Export_sample20240424_164810.txt' because it is being used 
by another process."

Out-File to a UNC path doesn't produce a terminating error in Powershell 7.4.2 or 5.1.

Expected behavior

For my example file. 
write-host $SampleCount
--2014
(get-content $destfile).count 
--2014

Actual behavior

For my example file. 
write-host $SampleCount
--2014
(get-content $destfile).count 
--a number ranging between 1995 and 2011 (depending on the number of times it failed to write a single line to the destination)

Error details

No response

Environment data

Name                           Value
----                           -----
PSVersion                      7.4.2
PSEdition                      Core
GitCommitId                    7.4.2
OS                             Microsoft Windows 10.0.19045
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response

Reproduisez les écritures répétées de Out-File -Append vers un chemin UNC sous Windows, en les comparant à une destination locale et à System.IO.File::AppendAllText. Suivez la manière dont Out-File gère l’ouverture et la fermeture du flux ainsi que les échecs d’écriture, puis vérifiez que les écritures ayant échoué sont signalées comme des erreurs et qu’aucune ligne d’exemple n’est perdue silencieusement.