First off, I'm not sure if this is the right place, but when I was fighting Arcann at the end of Battle of Odessen, He got to the final stage where he's supposed to jump up onto the top of the stairs and shoot lightning down at me, but he glitched and ended up back on the floor. This meant that when I gathered enough force power or whatever to bash his head in with the shield, it told me he was out of range, and now I have no idea what to do. I was told it works in Veteran, but I barely scraped through every boss on the way to him, and then couldn't get him to that phase when the time came. Needless to say, I'm super annoyed

U can trigger that bug by standing to close to the entrace. Better to keep the fight near the other side.

The very same thing happened to me last night. After battling him for over 15 min (getting the same message as you) I /stuck the fight and restarted it. This time I got behind him and kept my back to the stairs to the bridge, backing up a few steps when I could. This seemed to help trigger the events as they are supposed to happen, thus allowing me to finish the fight with shield bash and conclude the chapter.

Sweet, thanks! That helped and I was able to finish the quest finally