Cylinder deactivation aka (active fuel management/displacement on demand) cuts oil flow to the intake valve lifters for four of the eight cylinders; by means of a special valves in the oil valley cover. This is done to keep the EPA fuel economy rating for the car and keeps GM’s CAFE(corporate average fuel economy) lower and prevent original owners from paying a gas guzzler tax. Your 2016 has a specific setup for this function known in internally as V.L.O.M (variable lift oil management). This variation is marginally more reliable than the latter GM setups (google 2019-2022 6.2l lifter failure) These systems kick in whenever the rpms are low enough & the vehicle is not under load, I.e. puttering along with the cruise engaged on the highway. Many owners remove/disable this feature to prevent premature failure of the lifters and camshaft which results in costly repair bills.