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.