SecureString in file "randomly" stops working

It's really kind of odd the to decrypt just stops working, that sounds environmental. However, why are you doing this, this way...

Write-Output "Please enter the username of the SFTP user."$username = Read-HostWrite-Output "Please enter the password of the SFTP user"$password = Read-Host -AsSecureString$username | ConvertTo-SecureString -AsPlainText -Force | ConvertFrom-SecureString | Out-File "$scriptroot\Credentials.dat"$password | ConvertFrom-SecureString | Out-File -Append "$scriptroot\Credentials.dat"

... vs going one fo these routes.

$UserCreds = Get-Credential -Message 'Please enter the username of the SFTP credentials'$UserCreds.GetNetworkCredential().UserName$UserCreds.GetNetworkCredential().Password<## Resultspostanotepassword#>

Or this way,

Get-Credential -Message 'Please enter the username of the SFTP credentials.' | Export-Clixml -Path 'D:\temp\SFTPUserCreds.xml'Get-Content -Path 'D:\temp\SFTPUserCreds.xml'<## Results<Objs Version="1.1.0.1" xmlns="http://schemas.microsoft.com/powershell/2004/04">  <Obj RefId="0">    <TN RefId="0">      <T>System.Management.Automation.PSCredential</T>      <T>System.Object</T>    </TN>    <ToString>System.Management.Automation.PSCredential</ToString>    <Props>      <S N="UserName">postanote</S>      <SS N="Password">01000000d08c9ddf0115d1118c7a00c04fc297eb01000000bd0a9dd27ffa41419fb2b289838ebe6400000000020000000000106600000001000020000000ad2e4c96413a3e93e461f600e98f72aa5e3493bde41ac40491bfd4bedc462152000000000e8000000002000020000000e0016657a9f6e545b55876fa8095143c08046f1361baec0f693a1e823cc6ee0d200000006949857c09b23099dab66fdc3a7e4f7637970dbd3aa13be11fda7c8de63df70e40000000f9a266cbb34440f64d9a2bdeaaec3a6cda483138e0be29323ca0a523ac475e169793557e74dd208e3d4292aa4fbe5b90fc7023d41c4dd6d01f819366e0587885</SS>    </Props>  </Obj></Objs>#>

no decrypt needed, just pass the variable names

($UserCreds = Import-Clixml -Path 'D:\Temp\SFTPUserCreds.xml')<## ResultsUserName                      Password--------                      --------postanote System.Security.SecureString#>

Or this way

Get-Credential -Message 'Please enter the username of the SFTP credentials.' | Export-PSCredential -RegistryPath 'HKCU:\software\SFTP' -Name SFTPUserCreds$UserCred = Import-PSCredential -RegistryPath 'HKCU:\Software\SFTP' -Name SFTPUserCreds# Or just use Windows Credential ManagerFind-Module -Name '*CredentialManager*' | Format-Table -AutoSizeVersion Name                          Repository Description                                                                        ------- ----                          ---------- -----------                                                                        2.0     CredentialManager             PSGallery  Provides access to credentials in the Windows Credential Manager                   ...

So, even based on what you've read about SecureString, it's still a thing for most folks, though based on what I show above, I am not sure why.

Anyway, give one or more of the above a shot to see if that allows you more consistancy.