Odd discoloration on Agfa Record Rapid photo paper

Описание: The middle of the paper is still usable, but around the edges a brown discoloration appears during development. It can partially be wiped away.
The pattern of the stuff is like the box has been opened in daylight - but daylight exposure gives a black edge not brown.
This paper is from the 1970s, so i'm not too bothered by these stains.