This afternoon every time I have tried to accept an offer of exchange for an article I get an error telling me to clear the cache. When I do, I get the same error. If I then completely reload the browser and try again the offer disappears altogether. I have tried with articles of different treaties and I get the same error followed by disappearance of offer after reloading my browser. I don't believe the offers are disappearing because other people are accepting the offer just before me because it's doing it every single time no matter what treaty the article is for. I know from experience that even favourable offers for articles aren't accepted as quickly as favourable offers for resources so it is definitely a bug, especially as I get an error message when I first try to accept the offer.