I processed the 2 extreme exposures (overexposed = Dropbox - 2B9A4718.CR2) (under exposed = Dropbox - 2B9A4721.CR2) from a 5 exposure sequence taken on a tripod as a HDR image in Lightoom 6, the preview and processed and JPEG export image seems to still contain the green overlay used by the internal HDR process, see image below_. If I repeated the HDR merge with the extreme over-exposed image and one stop down from the extreme under exposed image (Dropbox - 2B9A4720.CR2) I get a normal HDR image. So it seems to be something wrong when trying to merge the extreme under exposed one, maybe lack of detail?
I reported this to Adobe, directly. We'll see if they can do something about it in the next release.