I *think* they fixed both but only announced the Colossus change, but I retired my Ranger playthrough to start a new Rogue one so I'm not 100% certain. I just recall looking in a log and thinking I had finally gotten Colossus, Hunter's and Duelling to all trigger for once. I think now they are all working as intended, but each can only be triggered on your Action attack once per round.
I just looked at mine and they're not stacking. I got the damage for dueling and hunter's mark, but not for colossus.
Very frustrating. Now I have to back up and choose beast master instead of hunter. Lot of time lost.
