I found another answer to this, which is to update to the NVIDIA graphics driver required by the very latest graphics cards (which mine is not). (My image processing PC stays offline at all times, and is stable, so I'm not in the habit of doing frequent software updates.) With the latest driver ...

Thanks for that, Catherine. The R5 only generates such images as JPEG, so I'll give 8-bit a try, too. That might be a better fix.

I suppose I'll look into a graphics card upgrade at some point, too.

By the way, I'm new here, and am very impressed with Helicon Focus, its processing speed, user ...

Update:

I have a workaround now, which is to disable OpenCL. Then each of the four methods progress to completion, albeit slowly.

So that's good, but my questions still remain. Given the processing time for such images, it would be nice to have OpenCL working.

With the latest firmware update, the Canon EOS R5 is now capable of capturing sharp, highly detailed, 400 megapixel images. It would be nice to stack these, but I seem to be hitting memory problems.

If I downsize them in Photoshop to 200 megapixels beforehand, Helicon Focus stacks them just fine ...