I was having trouble getting lower power to register using my multiple target attacker. The lower power effect would go off, I get the indicator of success, but it wasn't giving me credit for the event. I changed to a single target attacker and the lower power effect is recording properly now.
It almost seemed like with the multi target attacks the lower power was getting applied to the characters that were not the specific target required for event credit. Once I went to a single target attack I tracked how many times lower power went off and it started giving me credit for every one.

BTW, is there a character or two with Lower Power as an ability? I'm using energy talismans currently to get this effect.