Sorry to tell you but that is bugged, failed to work properly. I would usually recommend to reload the game as that does fix thing most times but seen that it's this mission and I also had this issue I know that will not work. I had 3 different playthroughs with Maxim to get different achievements and to play the Hoffman mission as that is when I first discovered it and came out also. Might have to re-do the whole thing or if you activate dev. mode you can manually reset this mission ... I should have did that first but didn't consider till after like 5 playthroughs and this happened again ...same thing will have to re-do the entire thing and hope it triggers properly. Had the same issues getting the win with maixm and kill maxim achievements also. won 3 times with him and killed him 3 times as well before any of that worked ... super frustrating and no, I did not invest a whole bunch of time etc just went straight to the point, won as quick, killed as quick etc as I could. Good luck and hope you get this to work but from where you are stuck at it will not magically fix itself if a reload does not help. Sorry