There's nothing to worry about. Your users probably had weak, spotty or no internet connection when submitting their feedback. Those items are now saved in your app on their device, and are silently trying to re-upload themselves until they eventually succeed.
Read this article: Shake's fail-proof mechanism
As for your users, they can invoke Shake and at the bottom of the screen under “More options” always see if they see any "Feedback pending sync" . Once again, they have to do nothing as all those items are already automatically trying to re-upload themselves until they eventually succeed.