We are aware of issue with login to appsheet.com redirecting to https://www.appsheet.com/template/@Html.JavascriptEncode((string)ViewBag.redirectTo) causing a 404 error screen.
Workaround:
Please navigate to appheet.com and navigate to My Account (My Apps)
Update: Triggering rollback. ETA to be complete in 30 mins i.e. 7:30 am PST.
Similar issue with login to appsheet.com, the popup with the login options does not appear after pressing the login button.