Why an app loses your poker history
Almost always the same way: the app needs you to log in, and one day the login stops working. The phone offloads the app, a token expires, an update resets the session — and years of results are behind a registration screen that will not let you back in.
Roll has no account, so it has no login to fail. Your sessions are in a database file on your phone. If this app disappeared tomorrow, your history would still be there, and you could still export it.