-WhatIf cleanup script says 13 expired archives but I only have 9 files total

tidying old backup archives on my fedora laptop (pwsh 7.4, emacs, and yes this is becoming a demo for my class). the script finds *.tar.gz older than KeepDays under ~/srv/archives and removes them, and i run it with -WhatIf first because i'm not an animal.

the folder has 9 archives across 3 subfolders. by hand i count 4 older than 30 days. the log says found 13 expired archives. then the foreach prints a few proper What if: Performing the operation "Remove archive" on target ... lines, but in between it dies with The property 'FullName' cannot be found on this object. Verify that the property exists. on the $item.FullName line.

i figured strict mode was being fussy about FileInfo, so i commented out Set-StrictMode -Version Latest. errors gone, count still 13. Get-ChildItem ... | Measure-Object by hand gives 9, which is right. so where do the extra 9 "items" come from, and why do only some blow up? (i can't paste a transcript right now, this is from memory of the terminal.)

the function in lib/Retention.ps1:

$cutoff = (Get-Date).AddDays(-$KeepDays)
$seenDirs = [System.Collections.Generic.HashSet[string]]::new()
$expired = [System.Collections.Generic.List[System.IO.FileInfo]]::new()

foreach ($f in Get-ChildItem -Path ... -Recurse -File -Filter '*.tar.gz') {
    $seenDirs.Add($f.DirectoryName)
    if ($f.LastWriteTime -lt $cutoff) {
        $expired.Add($f)
    }
}

Write-Verbose "scanned $($seenDirs.Count) directories"
return $expired

and in the main script:

$expired = Find-ExpiredArchives -Root $root -KeepDays $KeepDays
Write-LogLine "found $($expired.Count) expired archives"

foreach ($item in $expired) {
    if ($PSCmdlet.ShouldProcess($item.FullName, 'Remove archive')) {
        Remove-Item -LiteralPath $item.FullName
        $freed += $item.Length
    }
}

is -Recurse with -Filter doing something weird, or is the lib file getting loaded twice?