Gothic City Map

Running t15 end game maps and I've come across my first bug. I've completed the entire map and have saved the unique boss for the last bit of the map. Upon returning to the boss area I can not enter the boss area. There is an invisible wall that I can not pass nor can I shoot arrows into the arena. Will not be able to complete the map with this bug, no biggie I have tons of waystones but would at least like to share.