Hi,
You can use commands similar to below to close open file handles using Azure Cloud Shell:
$ctx = New-AzStorageContext -StorageAccountName "mystorageacctname" -StorageAccountKey "<account key>"
Close-AzStorageFileHandle -ShareName "mysharename" -Path 'archive' -Recursive -CloseAll -Context $ctx -PassThru
After the file handles are closed, you should be able to delete the folder.
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Thanks.
-TP