Subnet scan dumps System Names

I succesfully imported a spreadsheet with one /24 subnet (worked well).  System names were visible.  A few minutes later, they were gone. 

To test, I imported another subnet, again system names populated, and again they vanished. 

I imported the second subnet again, it repopulated the system names and they remained. I had disabled automatic scanning for this second subnet. 

After kicking off a manual scan for the second subnet, the system names are missing.