Currently, if you give a wrong answer, you get a red bar. But then, if you answer the item correctly in the same session, you get the negative feedback of that item’s level dropping.
My suggestion is to move the ‘level down’ indication to happen at the first wrong answer instead of at the correct answer. I can’t be sure, but I think that seeing the negative feedback on correct answer is causing me to make more mistakes by associating the correct answer with “red, wrong” feedback.
Sorry, perhaps I didn’t explain well, but the popup is not the problem. I like the popup! The problem is that when you get an item wrong, the “level down” popup does not appear. Instead, it appears when you finally get the same item right in the same session. So you get a “level dropped” indicator when you answer the question correctly.