It sometimes happens to me. Some fireballs are invisible, some are not. Don't know when exactly they decide to show up or not.

For me it's hit or miss.  Sometimes fireball is visible, sometimes not.

Though blizzard (or whatever that area effect snow spell is called) is displayed visually always.

I noticed this playing last night too.

The first fireball attack from my Sovereign would always be invisible, after that they'd show up fine. Except for the occasional one that seemed to originate from way off the tactical map, so the camera would auto pan and zoom and you'd see the fireball come from a far corner of the tactical grid - but it still got to its target

After the 1.05 release now sometimes I see all the ranged attacks.  Other times I see none.  I guess I'll play with video settings.