Cannot convert physical disk to vhdx (Hyper-V)

I have used Hyper-V Manager for more than two years to backup my two-partition external HDD to my computer (~600 GB [BitLocker encrypted] + ~100GB [unencrypted]). Here is a step-by step tutorial, on how to do it. This method was very convenient, since you are saving whole structure with full encryption and saving it to a single, expandable file (if used space is less than 700GB, the backup image will also take less space). Plus, if you want, you can attach it to your PC and use it as a virtual disk.

However, starting about two months ago, I could not copy the physical drive during the same method, always ending up with the following error:

[Window Title]
New Virtual Hard Disk Wizard

[Main Instruction]
The server encountered an error trying to create the virtual hard disk.

[Content]
Failed to convert the virtual disk.

The system failed to convert '\\?\scsi#disk&ven_st<some-ID>'.

[Expanded Information]
Failed to convert the virtual disk.

The system failed to convert '\\?\scsi#disk&ven_st<some-ID>': The request is not supported. (0x80070032).

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I have tried it on another Windows 10 machine - same error.

I have also tried Disk2vhd utility from Microsoft - also getting an "Error snapshotting volumes".

I have no clue, why this happens, since the disk is the same, with the same partitions. But it does not work anymore.

P.S.: if you are using some other method for backing up the whole physical disk/partition, please share! :)

Partial answer, for the Disk2vhd utility getting the error of "Error snapshotting volumes" :

Disabling the Disk2vhd option of "Use Volume Shadow Copy" allows to clone the drive.