Part way through the tutorial my magic suddenly went invisible. I can still cast it but I can't see it. I'll cast fireball, for example, and all that's visible is the ground lighting up as the invisible projectile travels to the target. The explosion, however, is still visible. The cold ring spell is similar; no visual effect but then every enemy in range becomes covered in ice. Meanwhile the basic elemental bolts that you cast with left-click go *partially* invisible. Most of the effect is gone but there's small, transparent grey "ghost" bolts still visible.

The weird thing is that this bug seems to come and go at random. When I first entered the marshes it was still happening, yet at some point in the middle of fighting I could suddenly see everything again. Does anyone have any idea how to fix this?

I believe that is due to something with the graphics. I cast the tech spell Overload. Sometimes, the effects you see will be invisible. I just let the spell wear out and cast again, and it is back. Same with some of the other effects sometimes.