I’ve imported a GEDCOM exported from FTM2019 that is about 350 individuals. The “new” persons added are not connected to any existing families. Each one is an island. No gender is assigned so they show up in Content Lists → Warnings. (I’m using AncesTREES if that makes a difference)
Unknown Unknown individuals are created when someone in a GEDCOM file doesn’t have a name. Since they aren’t connected do anyone, I’d just delete them.
Delete them that would have been my choice now I have found down loading descendants
to yield a large amount info run it dry earlier I got 1100+ new files on one click