what reasons are there for the scientific database score to go down?

I‘ve have had situations where i landed on a planet with rich resources yes the scientific db score jumped from 50% to 39% for example.

Whereas in other similar situations it remained at 85% 

Could someone explain the exact mechanism? Or is there a bug? Thanks

All the systems, including the databases, can be damaged if you land on a planet when you have a damaged landing system.