Lich Born invisible once when he respawned from the Abyss

Had a rogue exile near abyss in Holten, intermediate act 1.
Killed him, he respawned as lich born but then his model and attacks didn't load at all, he was just invisible, only visible on the minimap or layover by the icon.

forgot to take a picture or video.

Same thing happened to me on Act 4 with Sondar, The Lich Born

I killed him with shatter and his body got destroyed. Maybe that caused him to go invisible.