I have noticed second Spell bug by a Celestial Wizard of the Empire (see pictures 1 + 2).
I did an upgrade of this spell, but this spell never changed too becomes a better one (see pictures 2 + 3).
The description of this spell in the "Battle Effects" has been changed (see pictures 4 + 5).
I think that this is too a bug in this spell.
Perhaps you should test all the spells of the Celestial Wizard, that those spells haven’t further bugs.
I have the festtag update (see picture 6). And I never use any "beta" updates. Also I never use any mods.
And here the link from the 1st Spell bug: https://forums.totalwar.com/discussion/237761/spell-bug-the-empire#latest