Bottom surface of a model seems to be missing

[new3dprintinguser]

Hi, I printed a model downloaded from the internet. The raft layer was set to 2 or 3. After the print was completed, I removed the model from the coarse build plate of my Prusa i3 MK3s. Then, it looks like the bottom surface of the model was not printed as I could see the internals of the model. What happened? Any suggestion on how to fix this issue?