Wrong build number being inserted

Hi

We are using a Powershell script to replace the build number in an angular config file however even though the build number in TC is reporting as #44 when the replacement occurs it replaces it with #42 which is the previous successful build. The powershell looks like this:

$VersionNumber = %system.build.number%
$filePath = ".\Test.DocumentControl.Websites.Portal\src\app\app.config.ts"

(GC $filePath).Replace("{buildnumber}", "$versionNumber") | Set-Content $filePath

I'm at a bit of a loss?!

Thanks