Sander ''Szann'' Lipmann

Info from the source itself:

This is due to the intersector used by karma applying ray bias when it's continuing rays after hitting partially opaque surface. Mantra doesn't have this issue because it collects all intersections in one go. Unfortunately this behaviour in karma is unlikely to be changed any time soon. However, you can adjust ray bias and reduce its value until the artifacts are no longer visible. (If you're using Houdini build 19.0.458 or newer, you can try setting it to 0)

I updated Houdini to .458 and indeed a ray bias setting of 0 works

Oh and in .458 the refresh of the animations in the viewport is way better. Not 100 but at least no more full white blocks. Very workable now.

Thanks for mentioning the ray bias. It doesn't completely solve the problem but works in most cases.

Cannot imagine nobody has encountered any of these basic issues...