device usage and summary home network activity last 24 hours don't match up

Something on my network is using a LOT more bandwidth than usual. I'm normally around 500 GB/mo give or take.

This month in only 28 days (5 of which I was not here and nothing high-bandwidth was active, so really more like 23 days) I am using 926 GB and got a warning about going over the cap.

However, the xFi app doesn't show me what's using all the data! The summary shows "very high" pegged for the last 24 hours, yet if I painstakingly click through *every* device (even the non-active ones), none of them shows more than a blip of "very high" or more than a few hours in a row of medium/high usage, yet the 24 hour view shows it pegged, and given the nearly 2x usage of my household this month, I'm trying to figure out what's going on. My daughter got a smart TV for Christmas, so that is probably contributing, if not the culprit but even that device doesn't show activity during the day so I'm at a loss.

Here's a screen cap from the xFi app (web site shows the same) where all the profiles (every device is assigned to one of them) are all 0% yet it's "very high" the last 24 hours and my data usage is way higher than normal. I don't see how you can bill someone for this when there is NO way to debug what the cause is.