CB showed 46k hp left.

I attacked and he died. Collapsed and all attacks stopped.

I get a message that I did 65k dmg. That's 19k more than was necessary.

There was no cb death message. The cb screen shows he still has 2k hp.

The total discrepancy is 21k.

This is pure bull stuff. 

This needs fixed. Right away. It's inexcusable and unacceptable.  Period.

If my count is correct this is the 9th time this has happened to me.

Plarium, you need to take this seriously. There is a MASSIVE error in your damage calculations. No matter what your monitors show you there IS an error. There is no way to trust the calculations this game produces. An error like this could have been easily reproduced in other areas. Like, for instance, the high failure rate of high success chance artifact upgrades. Or every single fight in the game. 

Whatever system you have to verify this is, most likely flawed. In all likelihood your system assumes that the calculations are correct. And it is abundantly clear that they aren't. 

Your game cannot add 1+1.