Problem with plane painting please help

Hello to everyone,
I could not understand the problem I was having with the A320 painting. Can you help with this.
I painted A320 aircraft in the Blender program and as you can see in the picture, a different floor is formed in the tail. Although I have repeatedly cleaned old paintwork on the MODEL, I ran into such a problem. If I have a friend who has information about this issue, I would like him to inform me.
Thank you all in advance.