Today I hunted for hours with my mage, never failed on any spell, not even WOD, unless interrupted. That surprised me because I am not 120 Weaver yet, 118.8.
IIRC, at 117.5 spellweaving, you have a 100% success at WOD.
I have protection casted all the time. The only times I have failed ev and wod at 120 under certain situations -
1) When I get mana drained below what's required.
Not sure if mind rot would do the same but in theory, if you had just enough mana to cast ev and got hit with mindrot in midcast, the ev should fail if you don't have enough mana to cover the increased cost. Anyone know for sure?
Or maybe getting lmc eqm removed. Eg swapping to a suit with less lmc or even swapping your scrapper with a slayer spellbook with less lmc. Anyone know for sure?
2) When I happen to be dragging something in my cursor.
@Ivory, could any of the above have occurred when you failed the ev?
However, having said all that, wife fizzled 1 WOD yesterday fighting a renowned ratman (in the cavern of the discarded). She's at 120 spellweaving. Casted protection, so it is not caused by interupts.
Didn't take note of her mana level though, or any spell effect at that time. Not sure why it failed. Will have to test it more to be sure to see if the success chance has been lowered.