Please try to close the app completely before logging in again.
To do so, from the home screen of your device, double click the home button. Your open apps will appear in a list at the bottom of your screen.
Find the Chess.com icon in that list, and press and hold the app until you see a red (-) symbol.
Press the (-) symbol to close the app completely. Once done, try to reopen the app and login again :)
Today, all of the sudden, I can't log on to chess.com from my i phone. Help please.
Thanks.