We've been happily working with Sprints with Greenhopper until today when wierdness started. To begin with newly created issues weren't appearing in the backlog, then the backlog disappeared altogether (a fair bit of fiddling was going on to work out why the new issues weren't showing).
The underlying filter is showing all the issues correctly, but for some reason they just won't appear.
I'va had this a couple of times alright, there always had been an explanation eventually. On top of the filter there are some other selections which are doing further filtering, such as the fixVersion. So any items created not having a fiXVersion would not show for example.