Duolingo can be so difficult sometimes
Never before did i have so many wrong in one lesson as today, but still my lesson got gold, i increased in fleuncy and got two lingots!just thought was worth mentioning....
Don't worry, the site is working as it should. Seeing that material again will help you remember it, so the skill has strengthened to gold again. Getting lots of questions wrong shows Duolingo that you need to practise that material more often, so that skill will weaken quite quickly, to prompt you to practise it quite soon.
Not every lesson or concept is easy but they're all important. For the hard lessons, put your head down and just push through them. There's a reason why so many people never become fluent in another language and it's not because languages are easy. They take motivation, dedication, and patience. Good luck!
I've noticed this too. Sometimes I feel as if I haven't learned the material at all and yet it rewards me as if I had. I think it would be better if they changed it so instead of the lesson appearing gold straight away, it would have 1 or 2 bars, to encourage you to practice it more even after completion.
We all have our days where some lessons are harder than others. Don't let it discourage you. We all struggle sometimes. Learning a different language than the one you were taught is never easy. With practice and repetition, you'll learn it in no time.....and all those lessons that were once a pain will be a breeze! :)