I have run into some characters that seem to be very difficult for the android app to recognize. I am sure that there are more and when I find them I will report them here.
火 Its impossible to get this one right in the app. The same goes for any character with 火 in it, like 炎 谈 etc.
口 When written alone it's fine but when it's a 部首 etc like in 喂 喝 etc it only requires 2 笔画 to finish and not 3 like its supposed to be. And when you try to write the 3rd last line the app thinks that the 口 is already finished and that you are trying to write the next 笔画 in the whole character.