Thank you @RickHoppe
Unfortunately, sk118936 didn't help. I did however identify that VS uses a different logging server than VSX.
Here is an output of 'cpstat fw -f log_connection' in 'vsenv 0' context:
Overall Status: 0
Overall Status Description: Security Gateway is reporting logs as defined
Local Logging Mode Description: Logs are written to log server
Local Logging Mode Status: 0
Local Logging Sending Rate: 0
Log Handling Rate: 0
Log Servers Connections
---------------------------------------------------------
|IP |Status|Status Description |Sending Rate|
---------------------------------------------------------
|10.168.200.10| 0|Log-Server Connected| 0|
---------------------------------------------------------
However, 'cpstat fw -f log_connection' in 'vsenv 1' context shows a NATted IP:
Overall Status: 2
Overall Status Description: Security Gateway is unable to report logs to any log server
Local Logging Mode Description: Writing logs locally due to connectivity problems
Local Logging Mode Status: 2
Local Logging Sending Rate: 0
Log Handling Rate: 0
Log Servers Connections
------------------------------------------------------------
|IP |Status|Status Description |Sending Rate|
------------------------------------------------------------
|xxx.xxx.xxx.xxx| 1|Log-Server Disconnected| 0|
------------------------------------------------------------
I tried to follow sk102712 without any success so far. $FWDIR/conf/masters still gets modified after each policy installation (in 'vsenv 1' context).