Bug.

[SnailStalker]

Meteor Hammer's charge attack stopped working during the second boss fight. I'm pretty f*ing sure I had that guy dead to rights. Pretty assassinating experience after taking a break for awhile to not be able to claw my way to the "good ending" with my favorite party.

[Dr.Disaster]

It's not a bug, it's a feature

The Meteor Hammer's Special Attack are spell charges and they are limited in number. Once they are all used up you have to recharge the hammer with a red crystal.