This has happened for three of my characters for which Blade of Woe was formerly working, as recently as this morning.

The first was a couple of weeks ago. She was a vampire at the time, and both Blade of Woe and Feed were working fine (I could get both to trigger; it was just a matter of how close I got to the target; Feed triggers farther out from the target than does BoW, and if I wanted to use BoW instead of Feed, I could just move closer to the target to trigger BoW). Then one day, Blade of Woe suddenly stopped working. I can only get Feed to work on that character now.

The issue occurred last week with the second character, who was normal (non-vampire), and Blade of Woe worked fine, but as soon as I earned the Vampire skill line, Blade of Woe stopped working for her.

It happened with the third character this morning. She is not a vampire, and won't be, and Blade of Woe was working this morning until I hit level two this morning on the Thieves Guild skill line, and suddenly Blade of Woe no longer works for this character.
Strangely, I have another non-vamp character who is beyond level two on both Dark Brotherhood and Thieves Guild, and Blade of Woe still works for that character.

So it appears to my eyes that there is some kind of conflict happening between Blade of Woe and the Vampire and Thieves Guild skill lines.

Or, if there are any known conflicts with certain add-ons, if I could be made aware of what they might be (if any), I'd appreciate it.
I've disabled all of the add-ons I may have added within the last three weeks (most of the add-ons I run are ones I've used since I started playing, and as I've stated, this issue has only been plaguing me within the last couple of weeks, and only on three of my ten characters. I have Blade of Woe on all of my characters and it is working on the other seven; none of those are vampires, and they all have the Thieves Guild skill line unlocked from opening Thieves Troves, only, so they are all level one on that skill line).

Could someone please look into this? Thanks.

PC/NA, ESO+