There seems to be a bug where swapping difficulties will update the multipliers on the main screen but not actually multiplying the rewards by those amounts. I was doing some of the quests on warlord 3, the enemies had the correct warlord 3 health but my soul multiplier after the battle was wrong.
The game was showing a souls multiplier of 3.35 and I was doing quests, which are affected by difficulty.
I was getting 34 souls per battle and the game was only awarding me 80 souls, This would only be a 2.35 multiplier which is the same as normal difficulty would give, However the monsters I was facing had warlord 3 stats still. I then changed the difficulty to warlord 1 and the game was now awarding me the correct amount of soul. Seeing this I changed back to warlord 3 and the game was finally awarding me the correct 3.35 multiplier for souls.
I'm not sure what caused this, it seems to be the first time I swapped from normal to warlord 3 it didn't update the reward multipliers correctly, even though the main screen with all the kingdoms showed the correct multiplier. I even tried about 4-5 battles and it never gave me the correct soul multiplier. However the monster stats definitely were boosted correctly.