iOS Sync not working (iOS 9.3.5 and earlier, SMC 6.1.12)

Question

This is not a new problem to me: When I put my iPads into the SMC, everything is fine, 100% of them are in sync. The devices rest untouched in Tablet-Carts, charging. And now device by device runs out of compliance because the SMC-App does not sync anymore. I already checked https://community.sophos.com/kb/en-us/118792 but that does not solve that issue. Is it because the devices are sleeping and reside untouched in their carts? 
 /Detlef

SDU · Answer

Hi All, 
 sorry for the late reply. 
 The description of MDM Administrator is correct. The struggle with iOS is the following: 
 In order to increase battery life and limit data consumption, Apple iOS only allows the app in foreground to get permanent access to internet data and/or CPU cycles. All apps in the background are put into sleep mode and in the case of certain conditions, like low memory, these apps may even be pushed further into the background to device storage. This app management functionality is handled transparently by iOS in the background, with little to no way for an app developer to influence its behavior. Only a very select number of apps and features on the device get preferential treatment and are always allowed to execute instructions in the background, for example: telephony, SMS text messaging, navigation, and the built-in iOS email client. Other apps can request permission to run in the background, but as I mention above, the operating system will grant this access based on internal rules and heuristics and may even suspend the app altogether. 
 Therefore, it might be, that the app is completely terminated. 
 I suggest to remove the SMC app synchronization from the compliance rules, if possible. Instead, I would add the "Max. synchronization gap" compliance rule instead. For iOS devices, there are two types of syncs: 
 1. The app synchronization which is used to determine the rooting status and the location. 
 2. The synchronization of the mobile device management protocol which is used to e.g. install profiles, lock / wipe the device or install apps. 
 Hope that helps. 
 Best regards Stefan