Android OS used almost 2 GB in background one day

[AC Question]

I have never had an issue with data before, but I got a notification that my data limit for the month is almost up with 2 weeks left in the billing cycle. I checked my data usage and found that Android OS used 1.71 GB in what appears to be one day! (I don't know how to insert a screenshot here, but the graph showing data for the month jumps vertically). Any ideas what this could be? Obviously it was a one-time thing so it shouldn't have anything to do with auto sync or auto backup or anything like that, which would use data over time. I also checked and my last software update was October 10th, whereas this spike in data looks like it occurred around October 25th. Has anyone else ever seen this?