It's not motion blur. The blur at any particular point seems to be diffused evenly in all directions.

This points to poor alignment of the lens. Possible causes of poor lens alignment could be:

• An IS/VR/VC/etc. element at full deflection. Lens based image stabilization works by slight changes in the centering and/or tilt of the stabilizing element. This does cause what should be a slight misalignment of the lens. It's still beneficial if the amount of blur caused by misalignment is less than the amount of blur that would be caused by camera motion.

• A stabilization element that, for whatever reason, no longer returns to the default "centered" position.¹

• Lens elements that are not properly aligned, even when stabilization elements are "parked" at the "centered" position. This could include any of the elements in the lens, not just the one(s) in the IS/VR/VC/etc. unit, and can even occur in a lens without optical stabilization.

One such type of misalignment is called tilt. This causes the field of focus to be tilted with respect to the imaging sensor. Sometimes this is desirable for certain shooting situations. A tilt/shift or perspective control lens mimics the movements of view cameras to allow intentionally introduced tilt in a controlled way where all of the optics in the lens are tilted together. When only some of the lens' optical elements are tilted, the various optical elements are out of alignment with one another and the image will degrade, even in the field of focus.

Looking at the two examples, it seems possible that your lens is demonstrating tilt.

In the first example the camera is almost square with the wall. In the second example, the wall in the lower left corner is much closer to the camera than the wall in the upper right corner (which is softer than the lower right corner, but not to the degree of difference seen in the first example where the lower right corner is much softer than the upper left corner). If the focus distance had been adjusted to make the center or upper right corner more in focus, then the closer parts of the wall in the lower left corner would have been the corner slightly out of focus.

The source of tilt might be the IS element moving as it should to counteract motion. One way to test this is to turn IS off and see if the problem persists. A good practice is to turn off IS when shutter times are short enough that proper camera technique won't introduce motion blur.

But it could also be another of the lens' elements that is tilted. It could be that the IS unit itself is tilted when "parked". It could even be that the entire lens is tilted with respect to the camera's sensor due to issues at the lens/camera attachment flange or even with the image sensor itself not being properly aligned with the lens flange. It's also not uncommon for a lens to demonstrate tilt if the screws holding the flange ring to the lens body work themselves loose over time.

¹ Roger Cicala mentioned in one of his lensrentals.com blog entries that shipping certain IS lenses without "parking" the IS elements by turning IS off before turning off the camera and/or detaching the lens can result in a chance of breaking the tabs in the IS assembly that holds the lens element centered when IS is turned off. When the tabs are broken, the IS element is free to flop around, even when IS is turned off.