Powershell - Parsing HTML Table From Invoke-WebRequest

A bit strange your ParsedHtml seems to have an XML declaration, but you could try the function below:

function ConvertFrom-HtmlTable {
    [CmdletBinding(DefaultParameterSetName = 'ByIndex')]
    param(
        [Parameter(Mandatory = $true, Position = 0)]
        [Microsoft.PowerShell.Commands.HtmlWebResponseObject]$WebRequest,

        [Parameter(Mandatory = $false, Position = 1, ParameterSetName = 'ByIndex')]
        [int]$TableIndex = 0,

        [Parameter(Mandatory = $false, Position = 1, ParameterSetName = 'ById')]
        [string]$TableId,

        [Parameter(Mandatory = $false, Position = 1, ParameterSetName = 'ByName')]
        [string]$TableName,

        [Parameter(Mandatory = $false, Position = 1, ParameterSetName = 'ByClass')]
        [string]$TableClassName,

        # if there are no <th> tags, by appending this switch, the code
        # uses the first row in the table as column headers.
        [switch]$FirstRowHasHeaders
   )

    # Extract the table out of the web request
    switch ($PSCmdlet.ParameterSetName) {
        'ById'    { $table = $WebRequest.ParsedHtml.getElementByID($TableId) }
        'ByIndex' { $table = @($WebRequest.ParsedHtml.getElementsByTagName('table'))[$TableIndex]}
        'ByName'  { $table = @($WebRequest.ParsedHtml.getElementsByName($TableName))[0] }
        'ByClass' { $table = @($WebRequest.ParsedHtml.getElementsByClassName($TableClassName))[0] }
    }
    $WebRequest.Dispose()
    $WebRequest.Finalize()  # free the COM objects

    if (!$table) {
        Write-Warning "Could not find the given table."
        return $null
    }

    # load the System.Web assembly to be able to decode HTML entities
    Add-Type -AssemblyName System.Web

    $headers = @()
    # Go through all of the rows in the table
    foreach ($row in $table.Rows) {
        $cells = @($row.Cells)
        # If there is a table header or if we should consider the first row 
        # to be the header row, remember its titles
        if ($FirstRowHasHeaders -or $cells[0].tagName -eq "TH") {
            $i = 0
            $headers = @($cells | ForEach-Object {
                $i++
                # decode HTML entities and double-up quotes that the value may contain
                $th = ([System.Web.HttpUtility]::HtmlDecode($_.InnerText) -replace '"', '""').Trim()
                # if the table header is empty, create it
                if ([string]::IsNullOrEmpty($th)) { "H$i" } else { $th }
            })
            # we now have headers, set the switch to $false so the rest is parsed as data
            $FirstRowHasHeaders = $false
            # proceed with the next row
            continue
        }
        # if we haven't found any table headers, make up names "H1", "H2", etc.
        if(-not $headers) {
            $headers = @(1..($cells.Count + 2) | ForEach-Object { "H$_" })
        }

        # Now go through the cells in the the row. For each, try to find the
        # title that represents that column and create a hashtable mapping those
        # titles to content
        $hash = [Ordered]@{}
        for ($i = 0; $i -lt $cells.Count; $i++) {
            # decode HTML entities and double-up quotes that the value may contain
            $value = ([System.Web.HttpUtility]::HtmlDecode($cells[$i].InnerText) -replace '"', '""').Trim()
            $th = $headers[$i]
            $hash[$th] = $value.Trim()
        }
        # And finally cast that hashtable to a PSCustomObject
        [PSCustomObject]$hash
    }
}

and use it like this:

$GroupRequests = Invoke-WebRequest -Uri $URI -WebSession $session -Method GET

# the table doesn't have a name or id attribute, so use its index (guessing its the first table)
# in your example the table also does not have <th> header tags, so append -FirstRowHasHeaders
# if you want the first data row to act as column headers or accept that headers are created as
# 'H1', 'H2', 'H3' etc. Cells containing only whitespace will always be translated to 'H<columnNumber>'
$users = ConvertFrom-HtmlTable -WebRequest $GroupRequests -TableIndex 0 -FirstRowHasHeaders

# show on screen
$users | Format-Table -AutoSize

# save as CSV file
$users | Export-Csv -Path 'X:\Somewhere\users.csv' -NoTypeInformation