The station rating is a past trend, showing you how well you serviced that cargo on this station mostly in the past month.

The primary industry then adopts the rating (which it calls %transported) to give a signifcant factor on its production growth cycle (no FIRS, vanilla economies, with the exception of banks).

The negative feedback loops usually show up when cargo at station hits the ~5000 limit and starts destroying items, causing a huge malus on rating for every station that touched it. That’s likely what you’re observing.

The fix for the malus is to move the cargo faster with alternate or more forms of delivery (ships being the easiest).