I use the mobile app on my phone (Android, if that makes a difference).
If a thread has a lot of posts, I often find that as I'm reading down it, I only get what seems to be a random selection of posts. Eg when I open the thread it says there are 300 posts, but as I scroll down and read them, I can tell by the size of the wee scroll bar down the right hand side of the screen that there is no way there are 300 posts visible. Then I'll read a post and it will maybe refer to something the OP has said in a follow up post and I think 'I never saw her say that' so I scroll back up and there is no post except her opening one. Basically the whole discussion is disjointed. If I close the app down and go back in again, I might get different posts on the same thread 
I have the app on my tablet and it doesn't happen there, only on my phone. (Although the tablet one is almost unusable due to the number of sticky posts you have to scroll through before you get to the active threads 
)
Does anyone else get that?