My friend and I have also ran into this issue. I'll describe the important things we found:

1. Doesn't matter which morph, both are bugged.
2. We've noticed this yesterday, and only started testing today.
3. Yesterday we did Scalecaller Peak veteran. The first boss had something that also made my friend (Valcur, who is a templar tank) die automatically, his health was desynced. Perhaps the boss has a similar attack to jabs. Same happened in Gargoyle boss.
4. Breath of Life also has a delay. After you cast it some time, when combat ends (perhaps?) the effect happens even if the ability is not being cast anymore, and the healing too.
5. How it jabs/sweep bug seems to work: A freeze occurs if you spam your attack key, the one bound to jabs. The faster you spam it, it will freeze, at points, not always. You've to time correctly to have the jabs animation to occur properly, yet even if it freezes, the damage seems to still be there. Perhaps stacking, and then releasing after a while. Happens no matter with which weapon. Notice the freeze is very annoying and cannot be cancelled, it is a second or so and you can't do anything else while it is happening. Both on mobs and players. On vSP yesterday it was extremely annoying. We recorded a video right now to show you how it happens with both the skelly and ourselves dueling:

https://www.youtube.com/watch?v=RNKPHiLtYJk&feature=youtu.be

I hope this helps, if you've any questions, we'll all be up for testing out, ZOS. But we need a fix for this very soon.

@ZOS_GinaBruno @ZOS_JessicaFolsom @ZOS_RichLambert @ZOS_Wrobel

Cinbri wrote: »

And than it showing up some time later
https://www.youtube.com/watch?v=4rw1P85MQvo&feature=youtu.be

That pretty rough bug and seems happens not only with jabs.

Yea, have noticed it with just about all kinds of damage in Cyrodiil. Its kind of annoying, because sometimes it just happens, and you have no indicator, no reason to pop a vigor or rally heal, you just keep attacking, then boom, fall over dead. I think this may be an actual Combat bug, not just a bug of Jabs alone (Though Jabs is so buggy right now, it wouldn't surprise me if this was a jabs bug, and the Health Desync in Cyro is something completely different xD).

From ZunaRoath's post, it seems to be quite a severe bug, because on Valcur's screen shot both players have completely opposite position, in comparison with his clip showing him alive. It looks as if the bug also corrupts players positioning via the realtime servers..