Just stumbled over this thread now, thank you for your kind words gents, especially @JYW! Hope you have logged good hours on your P2012 in the meantime 🙂
@qqwertz The reason for the log-out usually is expiry of a token. The session is stored in a token (on the web, these are mostly called cookies), which will be refreshed the next time you use the app (or log-in to a website). If the token is not valid anymore, you have to log-in again. Now websites and apps handle expiration differently, browser websites are usually more strict, highly correlating with how secure the system has to be (e.g. banking website log you out after 5 minutes of inactivity).
But a long expiration time doesn't imply an unsecure system. It's a question of implementation, and usually there is not one token but two, plus additional security meassures.