A few minutes ago I played Drak'Tharon Keep(5 player(Heroic)) and I want to inform everyone that the instance has returned to an earlier state meaning it has it good old bugs back. I think it has something to do with the Servers being rescripted due to new Merge so it will probably be fixed soon, though for now I recommend Kicking 2 players and then requing RDF HC.
If you have encountered the same issue or have played it without problems, please update the information regarding this post.