From Wargaming: Our Developers have now fixed the issue with the XP bonus for the Valiant Effort reward.

In order to get the Mastery Badge when players have a defeat, players will need to have invested similar effort than for a victorious battle.

What’s more, the Bonus for Valiant Effort can now be received in case of a draw result.

We apologize for the inconvenience and we hope that you’ll enjoy the 3.4 update.

Thank you for your patience and understanding.

Your Support Team