Another vote to keep one logged in. I enter foods and activities all day long and it is uber annoying to enter the data and then have it look like it accepts it and then you lose the entry and it says log in. OMG, it's not like this is a bank account or some kind of top secret platform - it's just a diet log, lol.
BTW, I'm on a Mac, Safari. I'll look around for something that will make it appear a keystroke is going into the journal or something, perhaps a space. If the app senses you are typing it won't log you out.