Hi al vil,
Hope you're doing well.
It seems that the current avhdx file is being used by another process. You can check other virtual machines to see if this avhdx file is being used.
In addition, according to the error report, the chain between the avhdx and vhdx files is broken. You can click "Edit Disk" on "Hyper-V Manager" to repair the chain, and then try to start the virtual machine.
Best Regards,
Ian Xue
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