Safari deletes everything a website stores after 7 days of no interaction, and that includes this app's sessions. A Home Screen web app is exempt. A tab is not.
Install it: Share → Add to Home Screen, then open it from there. On Android: the menu (⋮) → Install app, or Add to Home screen.
If you know what you are doing and want to look anyway, add
?unsafe=1 to the URL. Nothing you log there is durable.