Thought that at first. I always check remember me. It will work sometimes for a week or more even through multiple locations. Then all of a sudden. When I'm going from page 4 to page 5 of a thread. It logs me out and asks if I want to download an app. (I really don't like the I pad app). This will happen a couple more times through the next hour or so then everything is fine for 1-3 weeks. I'm thinking it has something todo with site maintenance.
So you're using an iPad? I don't know how the iPad security works, and how it deals with cookies.