I reached 57% fluency last week and despite working on duo every day since, I can't seem to get to 58%.
Has anyone else found it difficult to gain percentage points?
I think there is a maximum somewhere that is much less than 100% because you can't become fluent by using Duolingo as the number of words is probably between 1250 and 1500. However, even 1500 words can be reasonably fluent, so the maximum might be about 65-70%.
If you make mistakes, I think that will lower your score but even if you don't make mistakes, the number of words you've been exposed to will depend on how many exercises you have completed.
Check your word list and for the number and their strength and that might give you more of a clue. And if you find someone higher than you, you could ask to compare. (I have 47% in Spanish with about 1250 words, although I was 51% at one point...)
So if you're currently plateaued on 57% it might be that while you're not making mistakes, you might be using the same list of words as there aren't many more, and so it's a random chance for meeting the ones you haven't encountered yet.
That's just my take on it.