It could be due to Preferences file corruption....or you found a new bug. Close LR and rename the LR Preferences file with a .OLD extension so you can restore it if not the cause. Try repeating the same workflow using the same files. Make sure to apply Library menu Metadata> Update DNG Preview & Metadata. You'll lose Pick flags and Collection association, but I don't think anything else. Remove the DNGs & JPEGs from LR and try again.
C:\Users\[user name]\AppData\Roaming\Adobe\Lightroom\Preferences\Lightroom Classic CC 7 Preferences.agprefs.OLD
Thanks Todd, Followed your advice, It worked as it should the second time around.
Another problem solved by the "magic sprinkle" on the Preferences file.
Glad to hear that fixed it! I've had to reset my LR Preferences file at least 2-3 times over the past year due to similar issues. When Adobe adds a new feature the current Preferences file needs to be "converted" to include that feature's "sticky" settings. It appears the conversion process can sometimes corrupt other settings in the Preferences file. I started keeping the OLD Preferences files as a log: