I post this here because of the character limit in the comment section.

From the mod's comment section: "IDK how my mod should change the line behavíour"

It's not the line behavior, it's the industry affected by station storage. The industry stops sending out cargo if it detects an overfilled station. That's normal. What happens with your station is that when the industry detects any amount of cargo sitting in a station at the beginning of one month, it will stop sending out cargo the month after that, implying the station has zero (or close to zero) storage.

But it's weird:

Truck lines work somewhat, possibly normally. I don't know how much storage space there is for trucks per length of station, since it isn't visible, so I don't know when I should expect the industry to stop sending cargo because the station is too full (as per normal game rules).

With only a train line, it's broken; it behaves as if there is no cargo storage.

If I set up the truck line so that it doesn't actually want to use it, due to waiting time being too high (e.g. only one truck on the line), the cargo diverts to the train line. However, it doesn't actually want to use the train line; it only does so because of the truck line. Adding more trucks to make the truck line operational does send some cargo through the truck line, but instead of running 100 % through the truck line, it gets split between trucks and trains.

I ask the author to test with only trains. I'm running a simple test setup here with only the station mod, industry button and no costs. I don't know if the malfunction is due to incorrectly configured cargo lanes for the trains, or the mod is asking for undefined behavior putting cargo for two different vehicle types in the same stucture. The train doesn't seem to have any problems pulling cargo from the truck storage, or vice versa, if both vehicle types are assigned to the same line. Whichever it is, it's broken at least for trains.