There is a channels configuration option like "First channel user sees". I expect that it is the first channel user sees after the first login. Now I see this "welcome aboard" channel first each time I enter the app. I would expect that the app remembers the last channel I visited.

Good point. I think those issues are unrelated, we just show the Welcome aboard message anytime you'll click the join linen link (which will work both when you're already in the community or not). I'll add a story to improve the flow here and not show the message if you're already a member.