My issue is similar. When I edit netflow sources under "ADMIN>>NTA SETTINGS>>SETTINGS>>NETFLOW SOURCES>>EDIT: I see two entries for each device.
I wish someone would comment on this post.
have started seeing this myself lately when Dell Servers will "loose" their virtualized interfaces and have been able to fix it by listing the resources and selecting them again. after this it polls the interfaces and they have come back up. Not a true fix but it treats the symptom.