I had same issue when executing Add-PnPListItem and Add-PnPFile on Azure Runbook.
I googled answers and finally found the following threads:

[https://github.com/SharePoint/PnP-PowerShell/issues/1541][1]

[https://github.com/SharePoint/PnP-PowerShell/issues/918][2]

They suggest a workaround for this issue is assigning output to a variable like below.

> $dummy = Add-PnpFile -Path $file -Folder $folder

It works for me. 
Your issue seems same kind, so it is worth trying.
Hope it will help!
  [1]: https://github.com/SharePoint/PnP-PowerShell/issues/1541
  [2]: https://github.com/SharePoint/PnP-PowerShell/issues/918