I developed an Enterprise app for a company which is running only in 4G network. There is only one application running in the device. The normal data usage is normally on average 200-300MB per month for each device for about 1 year already. The application and settings has not been changed after September. But it suddenly increase to about 1 or 2 GB per device since Nov.
To isolate the problem, I wipe out a device and setup as a new phone without any application installation. And I turn off the iCloud Backup, iCloud Drive, Photo and wifi-assist (actually the device will never use wifi). To my surprise, the data usage is still very high, on average, it uses about 100-200 MB per day.
I checked the celluar data usage. Here is the data usage since 4 Jan 2019:
Current Period: 1.2 GB
System Services: 1.2 GB
Messaging Services: 1.1 GB
Document & Sync: 49.0 MB
Push Notificate: 3.4 MB
Time & Location: 2.9 MB
By the way, previously the iPhone is running iOS 10.3 and upgrade to 12.1 in Dec.
Need your help on how to debug the issue? Thanks.
