• We have three phones on our account.
• All three phones show a cellular usage traffic event every six hours, like clockwork to the minute, when Data Utilization is viewed on the Verizon web site.
• This occurs even during the night when we are sleeping and no apps are actively used.
• As an experiment, I turned off 'Use Cellular Data' for all applications, but left 'Cellular Data' On, on one of the phones.
  • I reset statistics on that phone.
• As before, cellular data usage still occurs every six hours when I view the Data Utilization.
• However, none of the applications show any cellular usage at all (as expected, since they all have Cellular Data turned off).
• These unexplained data usage events vary in quantity from a few KB up to hundreds of MB, and in the past I have exceeded my limit because of this traffic (to VERIZON's benefit).
• WIFI assist is off, Notifications are off, Background App Refresh is off, iCloud Drive is off, Photos is off

I have seen other posts reporting this same observation, but I have never seen an explanation.

Is this Apple poaching data from me? 

Verizon clawing a few extra bucks out of me?

Something mundane (probably)?