several Unity and HDRP versions now and I’d like to get rid of it once and for all. Does anyone know what causes this? I can’t possibly be the only one that has this:
At some point in time I got rid of it my removing Screen Space Reflections. But in my current project even without SSR it’s there. It’s not Global Illumination either.
Thanks a lot for the help, much appreciated! 
Looks like TAA artifacts.
It is TAA related. You can tweak the speed rejection settings but in my opinion motion blur is broken in HDRP.
Yeah, it’s TAA. Thanks guys. But if TAA causes this, then what good is it in HDRP.
It looks like it’s missing motion vectors. Look at the object with the camera and go to Window > Analysis > Rendering Debugger > (in the menu that opened up: Rendering > “Full screen debug mode: Motion Vectors”)
Don’t move the camera, While the object is animating in front of you, do you see object motion vectors?
TAA is very important and HDRP’s TAA in 2020.3 and up is usually pretty good.
But it needs motion vectors otherwise it’s hard for it to do it’s job properly.
I think you need to set TAA quality to high and play with “speed rejection”
I’ve pretty much defaulted most projects to MSAA X2 / or FXAA mix or SMAA because of a lot of notable motion vector content in our scenes and projects.
Unfortunately there is more an more an apparent break between Anti alias solutions and the technologies that work well with one or the other.
-Anisotropic filtering forced on forces off MSAA
-TAA working great with skies volumetrics and clouds but not motion vectors.
TAA is a great step forward in most cases, however handling ghosting from motion vectors is something we’ll either have to accept (hopefully for now) based on the project or find an alt solution that doesn’t make a critical change to another feature that would also ghost less with TAA enabled.