It's not a DDoS attack. If you're using only Earthly Star and Indom to top off the party, very shortly after the holy goes off, then the party will be petrified.

Why?

The black hole cast places a debuff on all party members that slightly reduces maximum HP. This debuff wears off 2 seconds before White Hole finishes casting.

This means that heals after Fire III -> Holy must be timed such that the party is topped off AFTER the debuff wears off. You are healing too early, or you can cast an additional AoE heal after the debuff wears off.