Hi Tim,
We are experiencing the same issue with the T630. BSOD with the unmountable_boot_volume error. At first we only experienced when we physically disconnected the thin client from the power supply and reconnected it again. After a reboot everything worked as expected. We have experienced this issue with thin clients that came fresh out of the box.
Has HP responded to this issue already or are you still waiting for the solution? We are in contact with HP support and I hope they can help us with this. We are facing a rollout of 6000 thin clients in the next few months.
Would it be possible to share the case id with us?
If we have found the solution, I will share it right here for you.