Larian Studios Forums Divinity: Original Sin 2 Divinity - Original Sin 2 - General No XP - Driftwood (Minor Spoiler)

It's probably intended so you will be disappointed. I beat the game again yesterday and can confirm no xp from fish factory voidlings.

It is not as bad as I expected though. I still managed to get level 21 at end. If I min/max and slay every NPC in towns level 22 may still be achievable.