I believe... Without the boost you would have : 43382

I tried the xp boost and it do work.

Another thing.. It looks like you hit too high level Warlords. That will end up giving you less xp. You can go read about that somewhere here on this forum, also there is 3 vids on youtube.

Hello!

Thank you, COEUS, you are right again 

This item does increase the XP points properly. 

To see the difference clearly, try two battles: one with the activated item and the other without an item. Be sure to hit Warlords of the same level by Guardians of the same level. Then you will see how the points are doubled.