Photoshop: Merge to HDR Pro fails on large images with no error reported

Merge to HDR Pro fails on large images with no error reported. it appears to work up until the preview exposure is set. A good preview of the final output is shown. After completing the merge the output is just solid black.

A ~21,000 x 5000 pixel image with 4 images in the stack failed. When I reduced the size to 25% it worked.

See this thread for discussion and link to sample images:
https://forums.adobe.com/message/7203...