at this point i just wonder will u ever repair old karazhan,its over 1 year since this bug was first encountered yet both on forum and twitter there is no damn response… so what with that chess event afterall?
Hello Kriach,
If you are talking about the chest for the event not being generated after the encounter is over, that is a known issue that will be fixed in an upcoming patch.
If instead you are having problems in completing the event, you may find this article of interest 
If you have encountered a different problem though, please send it ove it via the “Submit Bug” option in-game, as Forums are not the appropriate channel for this kind of reports.