bug report in Hebrew
In the last lesson on Colors (on my mobile app), I was asked the same question about the color of owls (see below) over and over again. For a while the app was stuck at this question, asking it many times in a row, whether my answer was correct or intentionally wrong. The progress bar wasn't moving ahead (I think). Then the app went ahead to other questions, but still asked that question about owls once in a while, between new questions, until the very end. You can see in my screenshots that the same question was asked at different lengths of the progress bar. I only made two screenshots but the question was asked over 10 times.
Also, you can report bugs here: https://support.duolingo.com/hc/en-us/requests/new and use the report option at the bottom bar when you answer a question.