stuck ! same problem with my 2. profile. When I am asked to redo, the session will not finish.
hope someone can help me !! I have made a new profile, because the 1. could not finish sessions when I was asked to redo. Now I have the same problem.
If you see the option Redo for a lesson instead of Begin, the lesson is already complete. You can see a green tick mark on the lesson to confirm this. You should move on to the next lesson or the next skill if all lessons in the skill are complete. If seems lesson 4 of Verbs Present 3 is the next lesson you need to do.
That's the way Duolingo's spaced repetition is supposed to work. The algorithm makes sure the user regularly revises words which it determines are weak and can do with some more practice.
Each skill can have one or more lessons and each lesson teaches around 6 or so words. If the average strength of words fall below some threshold, the golden sheen changes back to the regular colour as a reminded to practice. Each practice session targets 8 - 10 words. If a lot of words are weak, you may need more than one practice session to re-gild the skill.
Edit: Also, just wanted to add. For revising completed skills, you can use the strengthen skill option instead of redoing individual lessons. Will add more variety to the practice sessions.