Larian Studios Forums Divinity: Original Sin 2 Divinity - Original Sin 2 - Help/Tips/Tricks Can't upgrade thievery past level 5,bug or intend?

As the title says I can't seem to upgrade the thievery skill for my ranger past level 5, is this intended or pheraps a bug?
Here's an image of the charactter in question, notice how the thievery skill doesn't have a + symbol on the right side

All social skills have a max level of five. Higher level can be only achieved with item bonuses.