On the home page, click the Create New Logbook button. Give the logbook a name like Test Logbook. A new green button shows up that says [object Object]. Clicking the button changes the URL to https://forester.radio/%5Bobject%20Object%5D/qsos. Reloading the main app page or opening it in a new tab doesn't show the [object Object] logbook any more.
(Something's string-ifying an object without a .toString method, or stringinfying the wrong object.)