I have a 1GB/month data plan and shortly before the month reset in mid-January, the data usage reported in Settings was abnormally high. It wasn’t that any of the apps had used more data, but rather the crux was operating system itself: More than 98% of my data plan had been consumed by System. No details were given as to what exactly System was using all that data for.
I had been traveling abroad to Bern, Switzerland in early January, and in the process meddled with a few settings, so my phone would less data during the time.
My first instinct was that I must have done something wrong when I reset everything upon returning home:
- Camera upload settings in the OneDrive app
- App update settings in the Store app
- System update settings under Advanced Settings
- Backup and Find My Phone under Settings –> Update & Security
Unfortunately, everything looked fine.
Then I tweeted @LumiaHelp, Microsoft’s Lumia/Windows Mobile support account. During our lengthy exchange, they pointed me to a few more things to reduce data usage I should check.
Unfortunately, they all looked fine too.
I once had an issue with my Wi-fi, such that even though I was home and should have been in range, I watched a movie on Netflix over the cellular network by accident. Hence I looked at a detailed log of when data was used, but it looked like those were times I was away from home, so it had to be something different.
As the month had just reset and I was back to 1 GB of data, I looked at data usage every hour every hour. Within a day, System had already used 123 MB. Overall it looked like System was using about 10MB/hour while the other apps were inconspicuous having used about 7MB in total.
I would not get very far with data being consumed at this rate. @LumiaHelp had the rather unhelpful suggestion that I could easily turn off my data connection from Action Center. I did that to save on data in the short run, but obviously this was not going to be a long-term solution. I was convinced now that it had to be a bug in Windows 10 Mobile. But @LumiaHelp wasn’t being helpful anymore.
At about the same time Paul Thurrott tweeted about the issue and a reply to his tweet pointed my in the right direction: Turning off message sync under Settings in the Messaging app.
Without message sync, my cellular data usage immediately went back to normal. I also found this discussion on Reddit about the issue. According to user JennMSFT it is on the Windows 10 Mobile team’s radar. So I’m holding out for a fix in a future operating system update. I’m not really sure what history sync was even working before. I haven’t seen my text messages show up in the Messaging app on my Surface running Windows 10.