Just moments ago I was fighting on a map with 3 enemies and when I played Firestorm the card his all of my party but only hit two out of the three enemies when the card says it hits everyone on the board. Anyone else have this happen to them?
How did you know it only hit two out of three enemies ? Did the battle log indicate that ? Or was one of them wearing Resistant Hide ? Or had Impenetrable Nimbus ? etc. etc..
I'm guessing that one character didn't take any damage and didn't have the card attach to them? In which case the most likely cause is that it was blocked. If it happens again, you can always take a screenshot or a copy of the battle log and post it here. I, and I'm sure many other people here, would be happy to take a look at it and either confirm that it's a bug or explain what happened and why.