I came across this kind of structure VERY often, structure with only 1 layer of block

Is this intended?

Perhaps it's a bit extreme. Those are the result of the ruins transformer being a bit harsh - I'll adjust this a bit later.

MC 1.11.2
Forge 2259
IvT 1.3.2.1
RC 1.2.10

@Ivorforce I would like to note this seems to be more evident when using any none default settings with the exception of the BIOMESOP generator.

What do you mean by 'none default settings ' and 'BIOMESOP generator'?

it wasn't only those two, I often find "flat" structure, of rather VERY destroyed one, like Castle, and multiple kind of house

They are supposed to be partially (or almost completely) destroyed. They're supposed to be ruins, if that is not clear :P

Ah ok, I thought there was a chance to find fairly intact Castle in the wild(as I saw some in old version) ;)
No problem though