It’s long been known by folks that examined the die (depending on rev) that the 286 has unused / inaccessible circuitry that cannot be activated in normal operations.
Some circuitry looked to be intentionally disabled and superfluous.

In the day it was assumed that the 286 was released incomplete with errata and broken functionality left on the table.

This article discovered some of that missing functionality but I don’t think it accounts for everything.

My guess is the remaining functions are actually broken needing a circuit redesign , would be interesting to have a clean room 286 with properly functioning 386 like virtual memory system on the 286