Server Overload, only some players are experiencing this issue due to too many actions occurring at the same time that server just cant process at a time..
i was told that same thing was happening for less than day or so when they opened EN 100 / speed 6/6 world due to too many actions.
When this happens please log out and log back in, the trades usually go through and countdown clock for them just seems to get stuck. For more specific help please send in a support ticket.