I'm of the personal opinion that OLMs aren't a great guide. They're a pre programmed estimation of the serviceability of your current oil based on driving factors such as temperature, load, cold starts, idle time, etc. It doesn't directly measure anything with the oil - 'tis but a best guess. Use a different oil / filter - or drive in some fringe scenarios, and the OLM will be grossly inaccurate. But I digress
That calculation which is numerically displayed to you as a percentage isn't your oil level. Only the estimated condition of the oil that's in there. Keeping it topped up is on you.
What oil are you running and for how long? High NOACK stuff is apt to burn off and evaporate. And low HTHS oils will tend to let more past the rings too. So oil used is one consideration
Next one is driving conditions. High RPM loads will burn more oil period. Both coming past the rings and through the PCV system. 4cyl mode will also counter-intuitively burn more oil due to the behavior of the lubrication system when it's activated. The reason for that is - the cylinders are still lubricated by an oil sprayer as they're still moving. But cylinders and rings need pressure to expand and seal appropriately. Fun fact: That's why long idle time is so bad and if you had to run the engine for say 1000 hours; it would cause you less wear to run for that long at 1500 rpm than at idle. Without combustion pressure, oil fairly freely makes it past the rings.
Could also be a manufacturing defect within the engine - newer rigs from almost all manufacturers are suffering from oil consumption problems as ring thickness, spacing are adjusted to trim weight. Unfortunately, unless it's truly hugely excessive, the dealer will just tell you to top up and go on your merry way. If it's more than a quart every 1k, then they'll give you some attention.
Edit: if you suspect carbon buildup in the deactivated cylinders - put some high octane gas in there and drive the everloving piss out of the truck. Hook up an 8k trailer and go up a few mountain passes or something. Get cylinder temps up and hold them there - will help burn up / clear out carbon. The higher octane is just to prevent spark retard and preignition as stuff heats up