MJP said:

I might have to think this through a little more, but typically you want your “rounding offset” (which snaps the texels of your shadow map to a fixed grid in world space) to be a translation applied to your projection matrix rather than being baked into the X/Y scale factors. Here's how I …

It's hard to tell just from one screen shot, but based on the code you provided your filtering kernel has a fixed size in shadow map space. The nature of shadow maps is that the effective size of a shadow map texel in screen space completely depends on how the shadow itself ends up getting projecte…

FYI that sort of issue would get caught by the D3D debug layer, and I definitely recommend enabling it for your debug builds.