Cant enter arena with boss "no clicable thing"

Subject. https://skrinshoter.ru/sUFzZtvagtA Screenshot.
Was running to enter arena but stopped to change minion support gem but boss started spawning I heard her voice. Probably that was a small lag which server received as I entered arena and closed it. Sad Ill have to rerun this map with no map modifiers (waste of time)