Where:
Skeleton cave in Barovia behind the Forest Fane
When:
It seems every time an enemy is killed with a Curse Song
What:
It seems every time an enemy is killed with a Curse Song there is not EXP given in the combat logs, It only happens for enemies killed by curse song
Recreate:
I was alone in the combat fighting skeleton lords and getting EXP for every kill except for curse song kills, to recreate should be easy enough to get an enemy that would normally give a combat log message to low health then cast curse song to kill them.
Ideas:
No idea how it works