Rest assured, you are not alone.
1.3 has affected me in a similar way. It breaks down into two main things: pop-in and frame rate jitters.
The pop-in since I installed 1.3 is nothing short of the worst I have seen in any game in over 30 years of gaming. Yes, it’s that bad. Where I had mild pop-in prior to the patch, I now have literal blobs of textureless walls in places like Rattay and Sasau. They load eventually, but when you ride into a town at a trot or gallop, you might as well forget it. Those textures won’t load in until I’m well past them.
The immersion-breaking result cannot be overstated.
The second issue is that the game plays downright janky since the patch. There is a jarring jitter in camera motion and character animation which, again, completely destroys any immersion factor.
1.4 absolutely must fix these issues. KCD is a fantastic game and I really hope to play a stable version of it someday, but there are too many other things to do then sit in Rattay square waiting for the Rathaus to render.
EDIT: I’m also playing on Xbox One.