Frost Wave is broken/stuck

[Razter]

The quest Frost Wave says to hit 30 enemies with 1 frost nova. However no matter what I do, it is stuck at 20/30.

I've done this on a couple of different maps and with agony on and off. It always stops at 20.

[Max]

This was happening to me too, regardless of map or density.

What finally worked for me was on Forgotten Viaduct, hitting a group of those enemies that only take 1 damage at a time.

[SilentStrike777]

this is happening to me as well

[XozzozaN-]

Yeah, it's a friggin' annoying bug. T_T Can't progress since it's stuck at 20/30. No other way to get the Ring of Frost too. Zzz.

[Infinite Oregano]

Yeah I'm also suffering this bug, it's seemingly stuck at 20/30, no matter how many enemies that I hit at once.
Actually, just now by pure happenstance I managed to get the quest done when I wasn't actually attempting it, by dint of as Max above said - it worked for me on Forgotten Viaduct when there was a large enough group of those ghosts that only take 1 damage at a time.