Listed words missing from lessons
Several times one or more of the words listed as being presented in a lesson haven't shown up in any of the sentences within that lesson. For example, 'siosúr' in lesson 7 of Objects, 'braillíní' and 'píosaí' in lesson 8 of Objects, and 'fiú' in lesson 3 of Adverbs. They show up later in overall practice, but not in the original lesson. For 'fiú', at least, I went through the lesson MANY times trying to see it, but no luck. Any ideas why this would be happening? Using the Android app.
I can't say for sure, but I know that if I'm consistently getting words wrong (including knowing the right word, but consistently not spelling it correctly or missing fadas), Duolingo tends to throw me the same words/sentences repeatedly until I can spell them correctly on a reliable basis... which tends to mean there are several words I don't see until the rest of the words in a lesson are at full strength. Basically, I've found that any "almost correct"s don't count against me in terms of XP or finishing the lesson, but they do count against me in terms of what I see next.
For me, that's a benefit, as I've always struggled more with remembering the correct orthography than remembering the words themselves... it just means it's down to me to keep tackling the same lesson until all the words in it are considered "strong" in Duolingo's estimation. It can get tedious, but in the end, it does result in my having the correct forms really, really solid, and able to remember why and when eclipsis/lenition/fadas are in play.
If you're spelling everything correctly - including fadas, lenition, and eclipsis where required - then you may have encountered some kind of bug in the Android app.