Learn mode unable to use.

When I was trying to use learn mode for revision, it loads for a long time and shows “Sorry, something went wrong. Please try refreshing the page. Apologies, an error occured while processing your request. Please try refreshing the page.”

After refreshing the page & restarting both my iPad and Mac, it still shows the same thing on both devices. The flashcard mode was fine, only the learn mode went wrong.