Void Beasts Dissapear

[Etaoin Shrdlu]

That is strange considering you had magical leadership (the starspawn guys) and plenty of it. Sounds buggy to me but R'lyeh is not a nation I have much experience with so what do I know...
Edit to reflect G.Dice's post (which was being typed at the same time apparently): If there weren't enough magical commanders leading the attack, the questioner would not have been able to bring that many magical critters into the play in the first place. So that's not the problem.