Issue with Lilith's Invulnerability in Battle

I am an active player of Diablo 4. I have reached level 130, fully upgraded my gear, and chosen excellent aspects for my character. However, I encountered an unexpected and extremely frustrating issue during the fight against Echo of Lilith.

During the battle, I managed to reduce her health by 99% in just a few seconds thanks to careful preparation and a well-thought-out strategy. However, when only 1% of her health remained, I noticed that it was not decreasing, regardless of what I did. I tried different approaches and skill setups, but nothing seemed to work. Additionally, I was shocked to see in the death statistics that my character was listed as „killed by an unknown entity.“

This leads me to question whether this was a bug that caused Lilith’s invulnerability at the last moment, or if I missed something in the mechanics of the battle. I could not find any information about this issue online, and I would greatly appreciate it if you could provide details about what might have happened. ps. this is in phase 1.

Hello,
this is the german forum.
But it is normal, that you can’t defeat Lilith in her phase 1.
She always enters phase 2 with a minimum of life.