Communication logs are not written at all. Until the disconnection, what is kept (in RAM) is the VPN IP address, your node IP address (obviously, otherwise there would be no communication at all with your node!). Additionally, the amount of exchanged data in that session and the duration time of the session itself. Finally, the average up and down "speed" of the last 60 seconds are calculated. All of these data do not affect privacy but at the same time help us to verify that a server is functioning properly. All of these data are lost forever when the client disconnects.
Only for troubleshooting purposes you can force the system (from your control panel) to keep logs of the total amount of exchanged data and duration time of each session for your user (if you decide to do so, you can anyway disable this function, which will cause deletion of those data). You can't anyway force the system to store your session IP addresses.