i have the same issue
Remove-CIVAppNetwork : 20/08/2019 12:51:13 PM Remove-CIVAppNetwork The operation cannot be performed because an input
object contains stale data. The object named 'External_DHPW-ProdIntrnlApp-2616' contains data which no longer corresponds
to the the actual state of the server. To resolve the issue retrieve a fresh copy of the object from the server and use it
to perform the operation.
At line:1 char:31
i ran this command
Get-CIVApp -Name 'DEV0-vap01' | Get-CIVAppNetwork | Remove-CIVAppNetwork -Confirm:$false -ErrorAction SilentlyContinue
And it worked. It removed the Network from the VApp.
Now I just need to install a New network to the Vapp