Locked out of Grimhaven boss fight

I know my character name is StinkyGrill, but even the boss went into the other corner of the screen and locked me out of the fight... this is RUDE!!!

Please add a portal to "Enter arena" if you cannot fix this bug :( This is the first time I started this map... already hard feelings against it!!!

Stepped in, stepped out to check if there is any more rares on map, went back to kill them, tried to kill boss... no access to the area...