If I"m understanding you correctly, both strikes you’re describing resulted in your heroes getting killed, yes?
That sounds like this issue:
Basically, the change was made intentionally in the 15.0 release, where heroes getting killed would not reflect damage back any more - the old behavior where they would still reflect that turn when they died, has apparently been a “bug” the whole time which was now fixed.
But, it’s now been decided to change things back to the old behavior, in the upcoming 15.1 release:
That doesn’t fix your 0 point battle this time, but at least in the future things will work as you would expect again.