I just started a playthrough where I've multiclassed Xoti.  I went to her inventory to giver her a fine breastplate, to see that The Vestments of Gaun had upgradability.  It comes with Guans Pledge which stems into two different upgrade options, but I don't know what they are.  It says "missing string 10706" on one and "missing string 10707".  Her armor has never been upgradable before, is it because I multiclassed or is there some kind of error??? *update, if you click on them they tell you the bonuses*

This seems to be new. As you said: it wasn't enchantable before.

Or do you use any mods that may have done this?

No mods, I did subscribe to a couple (steam), but I unsubscribed when I realized they would interfere with achievements.

In the meantime I learned about several new small changes. Seems we got a silent patch.

There is a mod that give upgrades to each items for companions; https://www.nexusmods.com/pillarsofeternity2/mods/260

Did you download and install the mod on the override folder?

I used the steam workshop. But as I said, I uninstalled all mods

I just loaded up a new game. As a single class Priest and multi-class Contemplative there were no upgrade options for the Vestments.  

Mmmm, with the steam workshop all you do is subscribe or unsubscribe. Maybe it doesn't uninstall correctly??

Seems the uninstalling of the mods didn't work out.

As for an update, my Steam launcher definitely updated the POE2 something the other day, just not sure what

Well at least I'm still getting achievements!! I'm trying to get them all!!

Mods don't block you from acquiring achievements. IIRC, the only option that blocks them is iroll20s in the console.