Please review this recent Field Notice. There’s a significant issue where a VMTools upgrade can brick your UC VM during a reboot.
Problem Description
After a Unified Communications server node is rebooted for any given reason, it will not boot the operating system (OS) back up. A reboot or power cycle of the server node will not boot the server node back up nor restore its services. The server node will remain offline and Applications Services will not be reinitialized.
The FN includes more details as well as a workaround in the event the system becomes bricked on reboot.
The latest SU’s for the various products include a fix.
Cisco Collab Engineering Tips 
Thank you Michael to highlight this one! I think it happens very rarely as it impacts versions for a long time and we never experienced this so far.
In the notice the explanation is not clear if the workaround part can be applied AFTER it’s bricked. They don’t say also how to check if we are impacted before rebooting and upgrading. Probably impossible…
Have you experienced this already?
Thanks.
Yorick