Based on their news update, that looks like exactly it:
About the compensation due to the failure◆

Thank you for playing Millennium War Aigis.

There was failure below between July 31st(Fri) 19:42 PM (EDT) ~ August 2nd(Sun) 22:38 PM (EDT).

【About the failure】
・The image that was suppose to be updated on August 11th (Tue) 2015 was shown due to the server error.

We will make compensation below for this failure
to the users who has used premium summons during this period.

【About the compensation】
We will return used Sacred Crystals for premium summons during the failure after
the maintenance on August 11th 2015 (Tue).

We sincerely apologize for any inconvenience you may have experienced.

We are working very hard to provide smooth, uninterrupted service.
We hope you continue to enjoy Millennium War Aigis.

The Millennium War Aigis Development Team