add-content produces stream not readable

Its an old post, but I run into a similar problem (using Set-Content instead of Add-Content). In my case, the WriteAllText Method solved that issue.

This should solve it for you:

[System.IO.File]::AppendAllText($csv_file,$newline)

Here is a PowerShell approach if you don't want to call the windows API. Put in a try catch block within a do loop to retry until successful.

    $isWritten = $false

    do {
        try {
            Add-Content -Path $csv_file -Value $newline -ErrorAction Stop
            $isWritten = $true
        }
        catch {
        }
    } until ( $isWritten )
}