The same sentence is showing up over and over again.
I had a full lesson of nothing but the same sentence: "もっとやさいを食べてください". (Please eat more vegetables). I got them right every time, it was just nothing but the same sentence again and again. It's not the first time this has happened to me, but usually it's two sentences. I'm guessing it's because Japanese is still in beta, but it's still really annoying to see the same sentence five times over.
Has anyone else had this problem?
I don't think it is a beta-problem, I think it is a bug. I came back here for Korean about nine days ago and I have seen people complaining about it both in the Korean and the Japanese forum. It is interesting, though, that it happened to me in Korean several times (although not for the whole lesson, only about four or five repeats of the same exercise) but it has not happened in Japanese - yet. When I started using duolingo the first time, a year and a few months back, there was a bug causing words to repeat because the system never registered them as reviewed. (People in the German forum were for example complaining about having to constantly translate different sentences about spiders, because the system erroneously thought that they had not reviewed the word for a long time.) My guess is that there is a new, but similar, bug living in at least the Korean and Japanese courses.
And to be clear: the main two reasons that I do not believe that this is a beta issue are 1) As far as I know a beta course is still a full course, it does have enough exercises, even though they have more things that need to be fixed. 2) If you encounter this problem you can review what you have studied and suddenly see several sentences, characters or words that you have never seen. Obviously they should have appeared the first time, instead of the repeated exercise. Conclusion: bug.
I, too, have had this issue in the first lesson to give place names (I believe that it is Introduction 4).
4 times each, I got "I live in Tokyo", Kyoto and Osaka. The only other things I got were Tokyo, "I live in Kyoto" and "I live in Osaka", once each.
From what Procellis said it probably is a glitch.
I also came across the vegetable sentence late last night/early morning. The same sentence over and over. I just copied and pasted my translation, and actually found it was a welcome relief from some of the very lengthy and complicated lessons I had to dig through recently. Meanwhile, some of these repeat sentences have also occurred in sets of 3 or, like the veggie sentence, with just one sentence. Usually two though.