You can resolve this issue by forcing sign-out of your Microsoft account, and by clearing Chrome cache, cookies, etc and after that signing back in to Excel Online.
To resolve your issue please follow below steps:
A. Sign out of all Microsoft Accounts
1. Go to the url https://login.microsoftonline.com/logout.srf and click Sign Out
2. Go to the url https://login.live.com/logout.srf and click Sign Out
B. Clear cache and cookies in Google Chrome
1. Open your Chrome browser.
2. On your browser toolbar please click on More, More and then More Tools and then Clear Browsing Data.
3. In the Clear browsing data box please select the tick boxes for Cookies and also other site data and Cached images and files.
4. Please use the menu at the top to select the amount of data that you want to delete. Also choose beginning of time to delete everything.
5. Now please click on Clear browsing data.
Finally please close your Chrome browser and re-open it and navigate to Microsoft Excel Online, and your issue must be resolved by now.