Hi. This isn't a bug - the spell is Shards, and it's a bit of a wild spell, might not hit, might hit several times. Each time a target is hit they take 4d20 damage, so again, damage varies a lot as well.
Generally against magic, Soak doesn't do very much. Evade is more useful, and especially a skill like Awareness.
Spectral wizards and especially emperors can be very dangerous.