This issue is far more complex than it may seem. I will try to explain why.
Applications that are allowed to run in the background fall into particular categories that implement particular features , for example geo-positional apps, voice-ip apps and apps playing music.
The ScadaMobile app is classified for this purpose as a Audio Player App. This may seem odd but it is not if you think on it. The app is able to actually play audio in the background and we demonstrated this to Apple some time ago. Nonetheless, the app provides a ‘tick’ sound that is played on the background to signal it is still running.
It is important to note that this is the only way we got approval to classify our apps to run in the background. We even tried to persuade Apple to create a new category for apps monitoring remote processes, which would require to do so in a non-stop basis, but they ultimately refused, so we took the mentioned (audio app) workaround instead.
This means that the app will keep running in the background for an unlimited period of time if and only if it was playing a sound when it went to the background and it will not not stop doing it. This makes possible to run the app in the background. The negative part is that *any* app is able play audio in the background, and as soon as another one starts to do so (i.e the iPod app) other apps are just removed from this condition.
Unfortunately, concurrent apps playing music is not the only reason that may trigger a stop of the SM app: low memory conditions and other undocumented situations may lead the iOS to stop any app at any time too. What we did is to detect when the app is about to be suspended and inform the user of such condition, so she/he has the opportunity to relaunch the app.
In your particular case, you should be able to attend at which condition caused it, and hopefully be able to reproduce it in a consistent way so you can try to prevent it when you need the app to keep running for a longer time. Any feedback on your findings on this would be very appreciated.