I do have the same problem, over 1000 words to practice but no "real" repetition. I am not extremely interested in 50 new words when I am struggling with the old ones...
By the way, it's in the English to Spanish course.
Is there anything we can do ourselves to fix/ help it fix? (I can't even send "bugs" because I am a free user, which to be honest isn't nice and I would consider feedback is helpful no matter by whom...)