Cracks in interior walls

[A.h.]

Hello.
I have a question regarding our interior walls.
They have cracks as you can see in the pictures below and above the windows. Similar cracks can be seen around several windows in the house. The cracks were there even before we bought the house 9 months ago and now after I have spackled and painted.
What do you think might be the cause of this? Should it be taken seriously and if so, what should be done about it?
It's a brick house.

 

[alm82]

What kind of wall is it? Old tretex boards?

 

[A.h.]

What kind of wall is it? Old tretex boards?

A bit hard to tell. But when I google tretex, I don't think it looks the same?

 

[Stefan N]

Looks like chipboard and that's how it is, plaster over everything if you want to avoid cracks.

 

[Donwoody]

Surely some form of wood board on the outer layer of the wall.
The only way, I would think, is to put gypsum over it
since the moisture in the house causes the wood to move, it often cracks open again over time.

 

[A.h.]

Thank you for the answers, then it is not something urgent that needs to be addressed, in other words, only aesthetic.