After you sign in, the app keeps a session on that browser so you don't sign in on every visit. Three things end it:
Inactivity. If you haven't used the app for about a day, the session expires.
Time. Even if you use the app every day, you'll be asked to sign in again 14 days after you signed in.
Signing out from the account menu, which also clears the support chat session on that browser.
When a session expires you'll see "You've been signed out". Nothing you saved is affected. Choose Sign in again and you're taken back to where you were.
Sessions are per browser and per device; signing in on your phone doesn't sign out your laptop. Assistant connections are separate from app sessions — an expired app session, or signing out, doesn't affect Claude or ChatGPT's access.
Signed out every time you reopen your browser? It's probably set to clear site data when it closes, or you're in a private window. Let app.justonce.ai keep its site data.