TImeout if session initiated by iPhone

Hi all,
I need some advice where to look at. I am connecting to a self-hosted jitsi-meet server (Debian Buster, jitsi-meet via repo), behind a NAT and nginx reverse proxy. Everything is working fine except that rooms initiated from the iOS app do timeout after approx. 5 minutes. I can spend hours in rooms established through a browser session but if the room has been generated by an iPhone it will (according to the logs) assume Elvis as left the building after about 5 minutes and close the session. Please advise if logs needed. Best regards and stay save!