There is an annoying bug with Elemental Affinity in terms of updating AP costs on skills. If you have exactly enough AP to cast a skill and you just generated a surface under you, the game won't let you cast the skill even though you have enough AP to do so.
Example: A pyromancer with Elemental Affinity starts their turn with 4 AP. They cast Flaming Daggers, with one dagger targeting themselves to generate a fire surfaces under them. The UI correctly updates to show the cost of Supernova to be 2 AP, but the skill is greyed out and unable to be cast even though you have enough AP to do so.
