This is a phenomena I've noticed since I started healing 2.5years ago. Every now&then I would finish a healcast on a target, in range, in los, under fire. And the heal wouldnt land.
I've always written it off as "he just got hit for the same amount as the heal" since its occurred rather rarely. But recently I saw a thread on wow forums, and it turns out that alot of players have been experiencing this same phenomenon, and everyone has written it off as "he just got hit for the same amount as the heal" It would be funny if it wasnt so sad.

The reason I made this thread on ej is because in the wowforum thread, the cm asked for help replicating this thing, and unwilling to let this off into the hands of the wow community I'm bringing it up with the elite.
Now, this is something that all healingclasses have experienced I think, I've gotten confirmation from everyone except a shammy, but I would guess its no different for them.

As far as I know, the test parameters would have to involve healing someone in combat with a mob/player. I would have tested it myself, but extremely strapped for time these days.

The faster we document this, the faster blizz can fix it.

I've only ever seen this happen when latency caused my heal to land after the tank was already dead despite having it go off on my end.

There's a multi-page thread about this in the WoW Bug Report forum. From reading through it, it sounds like there may be a legitimate problem, yet at the same time, it's hard to imagine such a bug existing in live without anyone able to document it and get that evidence to Blizzard.

I have been noticing the same thing, especially in arenas where such things stand out a lot more. I have yelled "WTF I healed you" more than once during an arena match. I always chalked it up to either a lag spike or the mentioned offsetting damage. Of course reproducing this will be hard but next time it happens I will check my combat log for evidence.

I've also had this happen. A lot, actually, and usually I don't see the heal land in my combat log despite the animation going off. I've actually been halfway through my next heal after a "failed" heal and my target dies.

This only happens to me when my target dies.

My latency is pretty consistently 60-80ms.

If you mean people dying even with the heal going off I would attribute it to latency.

My favourite death recently involved:
You die.
Magtheridon hits you for 10k (crushing).
You gain shield block.
Priest crit heals you for 6k.
You gain inspiration.
Inspiration fades from you.

Yes, I can 100% certify this is not due to lag. The reason its not documented could be because you could need both the healer and the healee to log it. I'm pretty sure it shows up in atleast the healers combatlog.

Edit: Example from 1hr ago: Me and warrior duoing steamvaults, been doing it for half an hour when suddenly a heal doesnt land. (he was at 70% hp)
Cant be lag, we're both under 70ping. Cant be lots of action, we were fighting two mobs in an instance all alone. I honestly doubt its the instance server, GB isnt the highest pop server I've been on and atleast not when it comes to instancing.

And also, this is something I've been noticing for 2.5years now, across 3 different servers and (well its hard to say) not limited to any particular high-traffic timeframes or sumt.

Not dying, just the heal... vanishing, just like the title says. My girlfriend plays a priest and she swears this will happen from time to time, even in big, slow heal situations where the tank shouldn't really be taking exactly equivalent incoming damage. I think it's been written off as such, or raid frames not updating quite fast enough... but we consistently ping about ~50ms, too.

I'd be interested to see more about this but... I have no idea how this could really possibly be tested. I can't seem to find the thread on the forums talking about this, either, can someone dredge that up?

Just another "me too". I know I have seen this and always chalked it up to lag (but even under pretty normal circumstances) or being hit by about the same amount as the heal, etc. Come to think of it I believe I saw this in an arena last night and I am fairly certain I was able to land a heal on the target afterword, so it was not a "target death only" situation.

This is all pretty anecdotal as I hadn't really planned on having to remember any of these situations.

Delayed... yes. Lost? Thought TCP/IP guaranteed in-order delivery of all packets, so you shouldn't be able to lose the message without losing your whole net connection.
(I'm not a network programmer - I've done only one project where I had to do any networking protocols and it was a roll-our-own over wireless, so I could certainly be misunderstanding, but that's how I understand TCP/IP)

Our tank has complained of this several times in Karazhan. It's not just on deathblows, either. I remember one particular Curator attempt got borked because one healer's heals were landing fine, but another healer's consistently bugged out and the first guy couldn't keep up.

I realize the obvious response is "the 'bugged' healer was asleep and making excuses", but you could see his healing animation play. It's just at the end of the cast, the tank's health didn't go up.

I'm inclined to agree with everyone else that this is probably just bad packet loss, or Blizzard would have documented it by now. But it sure is frustrating when it happens.

I've seen this before a number of times myself. A couple in Kara, quite a few times in Shadow Lab (my most run instance due to wanting the exalted mace). Not on deathblows, but rather, GHeal animation playing, losing mana... and nothing happening. No incoming damage, no deaths, but no heal. I'm beginning to wonder if it is related at all to the occasional desync issue I'll run into with certain players - at times, a player will randomly quit getting resses from me and my raid bars quit updating their status, despite the fact that I can see them next to me moving around and fighting, and cast on them otherwise, requiring a relog in order to clear the desync.

I'm fairly certain WoW would use a combination of various protocols. While TCP/IP is more reliable from a programming standpoint it isn't always the best option. UDP tends to be faster because its more of a "Send it and forget it" kind of architecture so it would be useful for things that are not crucial such as updating something simple like player position. TCP/IP would generally be used for something where you want a response from the server that says "hey I got that"

Anyway don't want to get off topic so back to the main point. My main priest sits 5 feet from me and has for 2.5 years, we've never noticed this phenomenom you claim.

We were talking about this in guild chat the other day -- I've never seen, but other healers have. Apparently, they said they notice it more when changing between targets to heal people, not when they're single target healing.

If this is part of the cause, it makes sense that I wouldn't see it as I never target anyone, I use mouseover macros for all of my heals and keep the mob targetted.

Sorry to derail it back to techical issues, but this could very well be specific to your computer. After one patch I had massive disconnect issues when logging on in a crowded area. I would time out most of the time. If I was in a raid at that point I could see every raid member getting updated one by one. Once I had synchronized with everything the game ran perfectly smooth even in the messiest of raid encounters.

After a bit of digging I replaced my network card driver and the issue went away. WoW was the only game that had the problem, and only after a certain patch. So Blizzard is probably using some "clever" network optimizations that can cause issues with certain configurations. This could be another one of those, where people with a certain hardware/software are getting excessive packet drops.

Just to clarify this.

Are you talking about heals going off at your end, not arriving at the other end, and the guy still being alive?

or

Are you talking about heals going off at your end, not arriving at the other end, and the guy being dead?

The first case i never really saw/never really paid any attention to,

The second case i however experience quite often and it can be rather frustratin.

First part, though the second usually follows, atleast the deathpart

You use UDP when you can tolerate packet lossage. This includes streaming media and certain fast paced games like FPS's - a few dropped frames is better than the overhead from all the ACKing TCP needs to do. TCP's peforrmance is aggravated in these situations even further if you don't disable Nagle's alg.

WoW is mostly quantized around the 1.5 GCD. I can't really imagine them using anything but TCP to ride on. It's harder to spoof (making their security tighter), the overhead isn't that bad in most situations, and you have much less of an issue with data lossage.

I mean, hell, UDP would blow up behind most "home firewall" devices since you'd need a specific stateful tracking module for the game's UDP protocol. WoW works without any kind of wankery like that [0], which leads me to believe it's just using TCP (which is usually statefully tracked).

Note that you can get data corruption and loss with TCP - it only uses a 16bit checksum as it's integrity checking system. This is worse than the 32 bit CRC provided with datalink layer protocols like Ethernet and no where near the level of integrity checking provided by MD5, SHA, and other "secure" checksum systems. Most higher level application protocols implement stronger data integrity checks like these in case TCP fails. In the context of WoW, though, they might not implement these sort of application specific checks, which could lead to these sorts of conditions. We'd have to look at the protocol itself that the client is using to communicate to the server and see what's happening.

Note that I wouldn't be surprised if the WoW client and server communicated over an encrypted channel. EQview or whatever it was a major exploit back in the heyday of EQ. All it did was analyze the network traffic between the EQ client and server and display a list of what mobs were where. Encrypting the client to server communication would seem to be the most secure way of preventing this sort of casual eavesdropping.

[0] The only port forwarding I need to do is for the Blizzard downloader.

I have felt like this has happened from time to time, but I've usually written it off to a debuff like MS reducing the heal by half combined with some hit and thus my 4k heal just disappears.

Removed.

It costs mana
It doesn't show up as healing done in combat log
target died

well for me i see my guy at low hp i see my mana being gone and the cast having finished, and I see him dead on the floor. I always blamed that as lag and the killing blow coming in just before the heal.