C# Pipeline.Invoke() not returning powershell collection

Question

On Windows 10, in C# I am trying to call a powershell script via Pipeline.Invoke() to retrieve all the disks on a network server, for each server on a network. But can't get it to return the data to C# when there are multiple disks on a server.

I have the following C# code:

foreach (var server in _collServers)
{
    Pipeline pipeline2 = runspace.CreatePipeline();
    pipeline2 = runspace.CreatePipeline();
    scriptCommand = new Command(@"C:\DEV\Monitor\Monitor\bin\scripts\GetDisks.ps1");
    CommandParameter commandParm = new CommandParameter("$server", server);
    scriptCommand.Parameters.Add(commandParm);
    pipeline2.Commands.Add(scriptCommand);
    var collDisks = pipeline2.Invoke();

    foreach (var item in collDisks)
    {
        var s = item.ToString();
    }
}

which executes the following powershell script (GetDisks.ps1), with ComputerName hardcoded to a specific server for now:

$disks = Get-CimInstance -ClassName CIM_LogicalDisk -ComputerName SERVER01 | Where-Object { ($_.DeviceID -ge 'C') -and ($_.DriveType -eq 3)} | Select-Object DeviceID, VolumeName, Size, Freespace

$disksout = [System.Collections.Generic.List[PSObject]]::New()
ForEach($d in $disks) 
{
    $disk = [PSObject] @{
            'DeviceID' = $d.DeviceID
            'VolumeName' = $d.VolumeName
            'Size' = $d.Size
            'Freespace' = $d.Freespace
        }
    $disksout.Add($disk)
}
$disksout

but it doesnt return a PSObjects collection into collDisks.

It works in the ISE (and every re-arrangement I try seems to work there).

It works if I run it for my local machine by removing -ComputerName SERVER01

$disks = Get-CimInstance -ClassName CIM_LogicalDisk | Where-Object { ($_.DeviceID -ge 'C') -and ($_.DriveType -eq 3)} | Select-Object DeviceID, VolumeName, Size, Freespace

It doesnt make any difference if I try using PSCustomObject instead, or creating the object collection different ways.