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