Free translation:
rare titan reward is reduced if you were not yet a member of the alliance when the titan appeared, or less than 12 days have passed since you received a full rare titan reward in another alliance
From version 38 release notes:
- Rare Titan Rewards are reduced if you were not a member of the Alliance at the time the Titan appeared, or if it has been less than 12 days since you received a full Rare Titan reward in a different Alliance. Previously, you needed to be a member of the Alliance 24 hours before the Rare Titan appeared.
Any chance is this your case?