Ritual boss always force me to death

I try running ritual boss with my friend and finish once in story mode. When I follow the green light after the 1st phase. At the end we met 2nd boss area and defeat the boss.
But when I do it on my own after the story there is continuous damage during green light for some reason I have like 1.5k hp and 5k es still very hard to reach the 2nd boss area. And once I reach 2nd boss area the boss area become dark and force me to death. Invited my friend to help but no one can reach 2nd boss phase. I try to re instance. Then the boss portal is gone. I cant finish this boss ever.

I try to run it again and it also force me to death after i reach 2nd boss area.
I waste 2 div for free

One more update. If my friend enter boss first. the bug is not occur. We can walk through 2nd phase without taking much damage. And when we reach 2nd area boss just stand there and start the fight

I have the same problem...