As it happens, I fell victim to this as a new customer when wanting to do a test restore. There were quite a few new variables with my test, so I didn't go straight to the backups being dodgy, but it happens that they came to the revelation of the Windows update from August causing the issue eventually. This was after a fair bit of back and forth, even going so far as going from a Hyper-V restore to a VMware restore and back. They seemed either reluctant to acknowledge the issue with the update preventing functional restores, or perhaps they weren't even confident at the time. I essentially helped them prove it by restoring a backup from the previous month successfully, which they seemed grateful for which suggests to me they weren't entirely sure at the time as to the cause.
Fair to say I am not the happiest new customer.
As to their note about it affecting VHDx restores, that isn't stricly true - I also couldn't boot my restored VM when it was in VMDK format either!
