Arbiter of Ash - Meditate Monk Skill issue

Hey folks, I just tried fighting the Arbiter on +1 difficulty, and after taking damage to ES, I noticed the Meditate Monk skill was greyed out on my bar and couldn’t be used. Is this intentionally disabled?

I had the same issue in the Arbiter fight. Initially, when I entered the arena I could use meditate and my ES would overflow like it always does, but somewhere near the end of the fight the skill was greyed out and I couldn’t use it anymore. Was extra frustrating as the boss was nearly down.