Sacred Blossom - Boss cannot be activated

I ran some Sacred Blossoms and after a few I had one that did not let me activate the boss. When I press the Heart of The Grove button my charakter runs to it but it won't acitvate. I tried multiple angles and from diffrent positions. I also left the area and came back and did a relog but with no effect.

Edit: After opening the next Blossom I realized that the tree or whatever structure that is under "the heart of the grove" button is usually glowing like a charismas tree. But it did not do that for the bugged encounter.