Larian Studios Forums Divinity: Original Sin 2 Divinity - Original Sin 2 - Bugs & Technical Problems [Bug] Can't Cast Elemental Affinity Reduced Spell

Actually, just on a hunch - I just did it again, but instead of using Pheonix Dive, I used battering ram.

Round starts, you have 4 ap.

Cast a fireball nearby to create a firey surface, and to use up 2 ap. You now have 2 AP left.

Battering Ram over to the fire surface you just created. You have 1 ap left. You are on a fire surface. Your Searing Daggers will cost 1ap while being affected by EA. You will not being able to use it.

So it's not Phoenix dive, it's mobility spells used to transition to an EA surface. Reloading the game clears the bug, and I can then cast searing daggers.