Try again unrated!
Users of CTS as a training tool must overcome a big shortcoming: If they, say, fail to solve every 5th problem, then time and again false patterns are engraved in the brain synapses. Just have a look at the history of a problem, then you find that the same tacticians failed again and again over the same problems. (I also did, more than once, even 3 times!).
So, today, I give myself a new rule. Whenever I lose points on a problem, I do it once more unrated. If I fail to solve a problem, I do it again twice. If I fail to solve a problem lower than my rating, I do it again three times.
Hope it will help. Time will tell.