Multiple ServiceNPCs showing up

Every time I return to the active lot, there are more and more nannies. At the moment, after a couple of in-game days, there are 5 nannies on my Sims' lot. And none of them leave.

When hiring a nanny service for children 4 nannies showed up then when I fired them all 4 were fired 

Now the nannies keeps spawning like the baby sitters!!They won't go away either like the baby sitters!!

Hi multiple nannies keep showing up to my property. I have six currently at my house.