When you exit an app simply by opening another one, the first app is still "running" in the background. Most apps do not update during this "backgrounded" or dormant mode, although they are still using active memory space. For apps that receive periodic updates from wireless services or the internet, this can give the appearance that the app's data is out-of-date or that the app has malfunctioned. The best procedure to avoid these issues is to "Force-Close" an app when you are not actively using it. This allows your app to make a new 'call' to our systems when it is opened again.
The actual process varies with the operating system and/or device type. However, below we have linked a video that provides some guidance on how to force close apps in most cases.
Link On How To Force Close An iOS App