"Unsupported Pattern" Exception When Executing Script, Not in Interactive Mode

I am attempting to perform a quiet uninstall of a program using PowerShell. Winget is used to initiate the uninstall process. The UIAutomation features are used press a single button in the UI that confirms the uninstall.

The script works when I execute it line by line, interactively. I've tested it this way multiple times. However, when I try running the script from file, or even just pasting the entire script block into PS, I receive this error:

Exception calling "GetCurrentPattern" with "1" argument(s): "Unsupported Pattern."

I've tried putting start-sleep elements after each action, just to isolate the problem, but that hasn't worked. I've tried running the script in different versions of powershell, I've tried running the script from the system context.

The script should open the program uninstaller and click the "Uninstall" button.

Full script:

#import required assemblies
Add-Type -AssemblyName UIAutomationClient
Add-Type -AssemblyName UIAutomationTypes

#find and run winget (script runs in system context and cant find winget, but directly referencing .exe works)
$winget = "$env:programfiles\WindowsApps\Microsoft.DesktopAppInstaller_*_x64__8wekyb3d8bbwe\winget.exe"
&$winget uninstall dropbox --Disable-Interactivity

#find drobbox uninstaller process
$DBUninstallProc = (Get-Process | Where-Object {$_.ProcessName -eq 'Au_'})
#wait for GUI to load
$null = $DBUninstallProc.WaitForInputIdle(5000)

#get root element
$root = [Windows.Automation.AutomationElement]::RootElement

#Create a PropertyCondition used to grab the Uninstaller Window
$GetDBWindowCondition = New-Object Windows.Automation.PropertyCondition([Windows.Automation.AutomationElement]::ProcessIdProperty, $DBUninstallProc.Id)

#Get the Uninstaller window
$DBUninstallerUI = $root.FindFirst([Windows.Automation.TreeScope]::Children, $GetDBWindowCondition)

#Find the uninstall button
$UninstallButtonCondition = New-Object Windows.Automation.PropertyCondition([Windows.Automation.AutomationElement]::NameProperty, "Uninstall")
$button = $DBUninstallerUI.FindFirst([Windows.Automation.TreeScope]::Descendants, $UninstallButtonCondition)

#Click the uninstall button
$button.GetCurrentPattern([Windows.Automation.InvokePattern]::Pattern) #.Invoke();