Some Mac OS and Google Chrome 89 users have been experiencing an "Error 11" page when in a class, especially when editing text on the whiteboard. Hitting refresh reloaded the class but the error page could continue to happen.
After investigation and confirmation from Google, this is a Google Chrome bug. When a Chrome version is updated to 89, it can reset the browser font size settings to 0. Having font size settings at 0 was the cause of the page reloading to an error page.
To stop the error from happening, update your version of Chrome to 90. If you're still using Chrome 89, go to chrome://settings/fonts and make sure both font sizes are set to a number above 0:
The errors in the classroom should stop happening.