The Night Hag has the following skill proficiencies:
Deception: 7, Insight: 6, Perception: 6, Stealth: 6
Challenge 5 means +3 proficiency bonus, so if we add the appropriate modifier, we should get the following:
Deception (CHA +3): 6, Insight (WIS +2): 5, Perception (WIS +2): 5, Stealth (DEX +2): 5
The actual values are all exactly 1 above the expected values, and I checked the entire SRD, it's the only monster with this particuliarity (I took the possible expertise into account to make this claim). All the other monsters skills proficiencies are either correct or been errata'ed.
Also, the Night Hag (Coven Variant) has the values I'd expect. (Note: this statement is now invalid since my reporting made D&D Beyond update the monster's stats to the book values.)
Furthermore, the Night Hag has already been through a round of errata, so I just don't get why those values are 1 point above the expected value without any text justifying it.
Does anyone have a clue? Is it an error? If yes, how should I report it?