So the boss arena of the new Lightless Arbor boss denies using movement skills at the very edge of the arena.
This is very deadly for the big AoE slam, where you need to react asap.
This issue in general is known already but never was an issue during boss fights.
Here is an example:
EDIT: For some reason twitch always brings down my second clip where I wanted to explain the issue outside of combat.
Here is a link to the whole stream with the correct time: