I'm not aware of any issues of this nature.
Indeed, installations of the Agent and VirusScan are expected to be without issue and without need for reboot.
The identified workaround of restarting the MSSQL service does not give me clues into what may have occurred to cause the disruption, unfortunately.
The only lead that sensibly comes to mind is in having the Buffer Overflow feature enabled. This monitors the SQL service's activity - and Microsoft are very adamant about how particular their SQL service is. They don't want anybody poking their nose into its business, and that's precisely what our BOP does
If the behavior is reproducible you'd want to engage our Support team to help work through some troubleshooting.