Sync of TCP connection table

You need to make sure connection mirroring is checked on the virtual server and the VS is part of the active floating traffic group. It depends on your requirements, but typically http traffic shouldn't need connection mirroring enabled.

Otherwise if that is all good, it is interesting that the active f5 does not share all active connections, just the new ones. f5 documentation says that connection updates should be sent to the standby unit with every packet or flow state update.

Could you test with a telnet session and show us the connection present and then missing on the standby unit?