Some weeks ago I decided that my recall was getting worse, so I started a new approach to duolingo: whenever a lesson turns non-gold I will repeat that lesson three times before moving on to anything else (even though it turns back to gold after the first repetition). I also take a break after each lesson set.
This seems to have helped me with my recall problem. If you're having the same issues maybe this might work for you.
Lessons don't get non-golden. The topics in the tree are called skills.
One skill contains 1-10 lessons - where most of the time you won't see all shown words.
Example 70+ words Verb skills:
If 10-15 words may be reviewed in a single session, it usually would take much more than 1-3 excercises to completely review the skill (e.g difficult words, weak words, all SR words from review backlog, etc.).
This is one of the reasons that my experience is, that vocabulary review works much better on Memrise, especially as I have to type in the L2 target language (all typing user script from Cooljingle), not simply translate in forward courses from e.g Portuguese to English.
Are you sure that when you repeat that skill two more times, that you don't get presented the exact same sentences from the 1st run (if skill is back to golden), but words are practiced in a very different context like adding different sentences???
IMHO you can not train "RECALL" with multiple-choice excercises or translating into your native language (isn't that called simply remembering, instead of recalling???).
There should be an difficulty-option to turn off multiple-choice excercises on DuoLingo. They are too easy, you can guess and you hardly learn from them.