I've reviewed the forums and haven't seen anything about this yet.
This has occurred in TWO separate companies which I've upgraded.
I've been managing SEP for 10+ years now and these upgrades are nothing new.
I haven't opened a case yet with Symantec, but wanted to share some information about upgrade risk.
The management console was upgraded from 12.1.7 to 14.x without problems.
Once I configured the clients to upgrade from 12.1.7 to 14.x via the management system, everything proceeded like normal.
The packages pushed to the servers and workstations and then stated that the client needed to be reboot.
Upon rebooting, the majority of the systems reboot normal, but out of approx. 160 servers I've upgraded so far, I've had around 15 servers and 3-4 workstations which have NOT upgraded properly. Some just keep stating the system needs to be reboot (2-3 servers) and the rest have NOT been able to boot up to the login screen.
The server OS I've had problems with is windows 2012 R2 and the workstations are running windows 10.x
For the servers, the windows logo would come up and the dots would spin in a circle forever.
For the workstations, they had a similar booting problem.
On both systems, they required multiple hard reboots until a message came up that said "software installation rollback" or something along those lines. After that you would get to the login screen where you could login OR it required another reboot.
The path I followed after that was uninstall 12.x software (14.x never fully installed), then reboot, sign in and install 14.x via an installation package and finally reboot once more.
I have NOT configured agent upgrade deployment for workstations in one of the sites as it is a huge risk right now.
Again, this was occurring in TWO separate companies which are not related to each other nor share any resources.