This post basically concerns two issues, with some overlap.
One, lately I am noticing that when I want to replay a story chapter for the achievements, more often than I have to start from scratch again. Regardless of whether I choose "Continue or replay episode" I don't get any of the familiar purple instances which you can use to replay for achievements, not without doing the whole episode from the first part again.
Secondly, I was wondering how other people feel about this, but wouldn't it be at all possible that, when you replay for achievemtns, to bring you straight back to the relevant bit that gives achievements? It can be very galling that sometimes you have an instance where you have to commit to 15 minutes of dialogue, fluff npc's before finally getting to the bit where you qualify for the actual achievements. Some of the achievements only take one mis-step to loose....to then have to go through the same 15 minutes of fluff and npc fights again is just taking away from the enjoyment of the game or the attempt to get the achievements. Living World Season 2, episode 'The Mystery Cave' comes to mind.