Selecting cluster in flashcards -> Something went wrong

I am very happy with the new update.
But I have a problem now with my flashcards.

When I select ‘flascards’. I have to select a cluster. When I click on ‘select a single folder/document’, I get the message ‘Something went wrong’
It’s very annoying because I use it a lot for my study! Actually I rely on it for my exams! It happens both in my Mac app and in the browser.

Am I the only one?
I hope that there will be a fix or something!!

Thanx for your help!
Best regards Mijke