Unreliable Health Bars
Players recently found out that the second boss of Murder Row deals "fake damage" to players. The green barrels dealt "damage" that would cause health bars to go down, which healers could heal up, but none of this was actually real. This was fixed last night and now works as intended, but it caused a fear that health bars aren't actually showing you correct information.
There is another case of misleading health bars. It's unclear exactly when this started, but it's happened at least in all of Midnight and The War Within. I'm using the term "Phantom damage" in this case because it's similar to the "fake damage" of the barrels, but slightly different. Fatpala and other theorycrafters reported this issue, but the cause and exact details weren't found until recently by Paoanii.
"Phantom Damage"
If you did Nulleaus or Azta'rec as a DPS, you may remember your health ping-ponging a lot because of how hard these bosses hit. Some players believed that Valeera just landed a well-timed heal on them, or a class passive healed them, but this is part of the "phantom damage".
All enemy melee swings are currently causing health bar issues. This mostly affects Tanks, but can affect DPS or heals when they get meleed. Whenever a melee swing hits a character, their health bar changes by double the amount, before rebounding and correcting itself. For example, if you have 100k health and you take a 45k melee swing, your health will briefly go down to 10k (making it look like you took 90k) before rebounding suddenly to 55k through no additional actions. This bug is more apparent when melee swings are massive (e.g. Protection Paladins, DPS on Delve Nemesis Bosses).
In this example here, you can see no additional healing and the raw hits of Azta'rec.
Health starts at 761,980
The melee hits for 372,388.
Health bar drops to 17,204 briefly and triggers the low health indicator.
Health bar rebounds to 389,592, which adds up correctly.
Health increases to ~390k due to Troll passive.
The melee hits for ~358k.
Health bar drops to 1 because phantom damage can't kill you.
Health bar rebounds to ~32k, which adds up correctly.
This appears both on raid frames and also on player frames, and on the base UI or using Addons, so it affects all players.
Why Does This Matter
Many players have noticed something has seemed off with health bars since the start of Season 1 and this discovery explains it. Many players were going to 1 HP and somehow not dying, which is very abnormal to hit exactly 1 HP. Now you know what's going on, and Tanks can be aware of this issue.
This is a very nasty bug, as it can cause some very reactionary play from both Tanks and Healers when the incoming damage is variable. The rubber-banding of the health bar makes it look like you're taking double damage and can make it look like a Tank just took an unexpected hit and almost died, especially when the phantom damage triggers the low health indicator, tinting the edge of the screen red. This can bait out external cooldowns such as Time Dilation. If you were a healer and you saw the raid frames in the above clip, how would you react to seeing a health bar look like that? For personal play, you may feel like you almost died and may panic personal or Health Pot or Healthstone, wasting it when you didn't need it.
