Arah P2.... again & again
This is an extremely common bug.
When the Bone Wall is still up, your entire party needs to wipe and after everyone is dead, respawn at the waypoint. The Bone Wall will then be down, and you can attempt to fight the boss again.
ANET is probably never going to fix it, as it’s a bug, and it’s a not related to the gem store or the living story. They will, however, ignore the kitten out of your reports, so please don’t waste your own time sending reports ANET probably isn’t even going to read, much less act on.