Ugh. I know what this is. You, sir, are a genius for spotting this.
There has been a bug for months. When a creature died, it died at least twice...
...but the reward code was broken, so creatures never dropped the correct rewards - just a single one. Twice.
I fixed it.
This broke the multiplier code. I will fix. Thanks so much!
[Edit: (sigh) fixed!]