Single-family house 1 year old water is pressing in - what could it be?

Good evening everyone,

Well, one year ago we bought the detached house built in 2001..

At first everything was perfect, everything was measured, all the walls in the basement dry, no abnormalities, and now one thing after another..

Now I noticed in the stairway or descent from the garage to the basement that the stairs have water stains?!

Strange that it wasn't visible last year, after all it was wetter then!

What could be the cause?
What can be done?
Could the previous owners have known about it?

Have you changed anything?

Is the drainage blocked?

hello Tom Tom

We have only filled in a bit of screed at the door upstairs

Could he have pushed away any slide? So that rainwater flows behind it, or clogs a drain?

if after a year something is bothering you then you will have no chance

Could it have pushed away some foil?
So that rainwater runs behind it, or clogs a drain?

This is how it looks from the outside