@Koen Yeah i feel this is the case too, it almost works but at certain positions and angles entire coarse voxel regions are culled as can be seen below in this video:

https://i.gyazo.com/d9453d12ceffc9635772a8e6481c4b4f.mp4​​

My only guess is the ray must jump into the wrong occupancy map voxels which returns a max alpha below the threshold so the region is culled, but im unsure.

If anyone is interested or has ideas the code has been moved to here:

https://github.com/James-Emmett/DirectVolumeRenderer