The poor population are missing

[Igotsomefirecities]

Right now I'm building a city in sandbox mode in which I have a combination of poor, middle, and rich inhabitants with happiness of 100%.Everything went well for the city until when i'm continuing to build the city, the poor population dropped to 0.Is there any explanation to this? ( Ratio Poor:Middle:Rich = 0:6:8 (+-140k pop))

[PBbunnypower]

Well my assumption is that everyone became more wealthy and poor people moved into rich houses after their needs/demands were met.

[Tonyc403]

Did you set the buildings yourself? If snot as your city grew read what the dude above me said .
Now if you set the buildings yourself and in settings have that feature turned on. They'll stay