Thanks for your advice Christopher. I'll contact them and see if they can help me somehow.
I was hoping not to find something like this on the internet but sadly I did... I am having the exact the same problem with this combo (XT2 + 16-55). Sometimes I get incredible sharp shots and other times I get these soft/blurry images - with different shutter speed and aperture settings. So I guess my lens is a bad copy too. The worst thing is I bought it used while traveling in the USA so no warranty and probably no chance to have it repaired here in Brazil. I just feel so sad right now...