I am experiencing exactly the same problem with story disconnects. I am a returning player and want to change main so I am trying to get my ranger through the story quests. I was doing the Last Chance, the last part of One path ends, just before the Path of Fire storyline starts and I got to the end of the storyline 8 or 9 times, across three days, before I disconnected in the same place each time. I ticketed ArenaNet but no response. I finally completed it but now it has started happening on Night of Fire, I get to the end of the scenario and I have once again disconnected on multiple occasions at the same point. This is very frustrating I wish they would give you a complete on killing the boss/completing the objective and not wait until the RP scenes/cut scenes are over as the problem seems to be during these. Even allowing a short time to reconnect would resolve some issues.