[NXTwoThou]

I've got a 950(through work) and while talking to someone about Mint, I went to go look at my own data usage. I was shocked to see I'd used 14.3GB in the last 30 days. 1.61GB on AT&T. When looking at details, AT&T shows 1.32GB for "System" and 7.97GB for WiFi. I jumped on AT&T's site to see my previous data usage and October was kind of high(I was on vacation for a week, so that makes sense), but the previous 6 months were all half a GB of usage.

How do I track down what "system" is doing?!?

[SlideWRX]

It might have been a system update; those seem to ignore the wifi only download rules. pretty much any MS software will do this; camera updates, firmware, OS updates, things like the maps software, etc...

There is a 'Restrict background data' option in the Network & wireless -> data usage settings. try that, and/or see what apps have background data permission. search 'background' (edit: under privacy settings) to get to the setting to turn permission on/off.

[NXTwoThou]

All the apps I use are listed in the data usage. For AT&T, "System" is 1.14GB while the next highest is Facebook with 87MB. For WiFi "System" is 7.51 GB next is "Microsoft Edge" at 3.55 GB, Facebook at 1.24 GB, and Groove at 279 MB, OneDrive 245 MB. "System" is greatly disproportional to any of the other categories. I've gone ahead and turned on restrict background data, hopefully that'll stop this giant bleed that's going on.

I think I've actually identified the culprit though. While going through everything that could count as "system", I went to backup and found that Skype was backing up 1.19 GB, Instagram 395 MB, and Groove 404 MB. I just plain gave up on Skype and uninstalled it. I also turned off Groove and Instagram for backing up. If it was backing up every day, "System" will now use nearly 2GB less. Not sure why these would suddenly balloon when I'm looking back at data usage for the year and it just started two months ago. I'm pretty sure all of the disastrous Skype updates have a big part to do with it.

Anyone reading this should double check their data to see if they've suddenly ballooned too.