not reachable after some stand-by time
Mobile client, f-droid without GCM push, dhtproxy and permanent notification enabled.
Receiving calls seems to work first, but after some hours it stops working.
A guess: Is the dhtproxy properly sending keep-alives to the clients every 14 Minutes? (To avoid NAT Gateway timeouts. Most mobile devices access the Internet through a device operated by the mobile service provider called a NAT (Network Address Translation) gateway. These will typically time out an idle connection after 15 minutes. https://www.isode.com/whitepapers/imap-idle.html)