What you were expecting to happen, and what actually happened
I was expecting to get 140 souls after battle, plus 100% armor bonus and possibly 45% statue bonus. All of the matches in Raid Boss, up to the 4th Boss (so far) are only giving 128 souls.
How often does this happen? When did it begin happening?
Only doing it in Raid Boss.
Steps to make it happen again
Play Raid Boss.