PowerShell Component Monitors - Not Defined

Are you using the "test" button in the "edit script" dialogue? If not you tend to get errors like this regardless, it formats the thing receiving the output

Try moving the endquote on the Message line to  "  Write-Host "Message: $ListsEqual"   "

Script seems like it works in general, though I've no idea why the if doesn't error

So on the example you gave above, it looks like on both of your Write-Host for message, you have the quote too early.  In theory it should be:

Write-Host "Message: $($ListsEqual)" where you have the end quote after the semicolon.

I normally like to start with my code in Visual Studio Code or another PS script editor, to validate the logic itself works.  I then run the script against the host first to validate my results.  Normally commenting out the exit blocks.

So are you running into not defined on just this script, or any powershell script?

I normally start my process with a simple:

Write-Host "Message: $($ENV:ComputerName)"

Then I pick my destination node and credentials and run the test.  This way I can verify I'm either A. hitting the right host (remote execution or polling method are normally the likely culprits) or if it just fails outright.  Which if it just fails, then I try a different node (which I know remote PS calls work on), and if that is a problem then I know i have something bigger going on.  If I see that systems name, then I know its a local host issue.  Once I validated that, then I remove it and start to build out the script chunk by chunk.  Outputting each call to a message, and then once I know my variables/counts are working correctly, then I branch into the final If/then logic.