You are right, there was an issue with the config file. The elux manager added a section line "[ ]" above the rtav.codec line and that seemed to make the client ignore this setting. I removed the section line and restarted the client. RTAV worked instantly.
Thank you for this workaround!
Can you tell if this will be fixed - so a workaround is not needed anymore - with a future client version?

Best regards

Andreas