I understand that you are formatting some disks attached to a Secure Boot enabled VM then running Set-AzVMDiskEncryptionExtension with the EncryptFormatAll option to apply Azure Disk Encryption. Afterwords you are attempting to mount the disks again but getting the above error. Please let me know if I am missing something.
When you use the EncryptFormatAll option the data and the filesystem on the disks will be deleted. If you are attempting to recover data from disks where this option has been run that will not be possible, you will need to restore the data from a backup. I hope that is not the case and your data is okay. Please read through the details here and let me know if there are any more questions.
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