I have reported this as a bug already and it has not been fixed, getting the same error message repeatedly when trying to review Italian courses, and it’s been ongoing for quite some time. Sometimes I’m able to review a few words from this link, but usually it’s the error message or it will give me like 8 words to review and then it’s the error message again.
Just to be clear: you have this error on the web?
I have the message (or something similar) on the Android App. Usually it goes away when I study one other word by using a different ‘game’, e.g. if the error happens during Review, do Learn New Words or Speed review and vice versa. Does this workaround work for you?
You might try to ignore the next word you want to learn - perhaps then it loads. Later unignore it.
The levels now displays correctly the total number of words. Each level needed to be updated manually.
For those who experience this issue and are contributor or creator of their course, you’ll need to edit each level which contains this bug and do a small change. In this scenario, I swapped the two last words back and forth then saved it. This will update the level correctly.