Time: 28th February, 20:00 GMT, though could happen any time.
Frequency: Sometimes
Monster name: Vortexer.
Party or solo: Party, 8 people.
In-game time: Any.
Area and coordinates: Alexander - The Cuff of the Son (Savage)
Steps:
1. Get to a certain point in the fight, multiple times.
2. The mechanic known as "Compressed Water" fails its check, explodes and proceeds to wipe the raid.
I am aware this bug is already listed in the Accepted Bugs thread, but I have additional information which may help solve the issue. It seems very likely that the Compressed Water buff is meant to appear on anyone who took the damage of the water effect, except for the initial target- it explodes if the initial target gets it, because this should mean the initial target was the only person who took the damage of the water, and thus executed the mechanic improperly, and thus wipes the raid. However, the Compressed Water CAN appear on the initial target after the water damaging effect, thus causing the wipe. This may happen because the debuff that follows the water damage that is intended to appear on the initial target- known as Water Vulnerability Up II- appears at the same time as the following Compressed Water debuff, and thus the second Compressed Water debuff fails to find the Water Vulnerability Up II following the effects of the first Compressed Water, and thus has a chance of applying to the initial target- the next tick, however, the game sees the Water Vulnerabiltiy Up II debuff on the initial target, as it should be, and the next Compressed Water debuff on the same person, and wipes the raid. As an example, if 3 people were to be damaged by the water damage of the first Compressed Water, there is a 1 in 3 chance of the initial target acquiring the next Compressed Water, which wipes the raid. Because this mechanic occurs multiple times in the fight, assuming there is an equal probability of each person acquiring the next Compressed Water debuff, this means there is a 74% chance of the raid wiping for no reason other than the bug, every single pull. It may also be that the following Compressed Water debuff fails to include the line in its coding that makes it exempt from reappearing on the person who had it previously, such as if it checks to find the Water Vulnerability Up II debuff. I hope this additional information helps you solve the issue.
Additionally, assuming the Vortexer has the Compressed Water mechanic in Alexander- The Burden of the Son (Savage), it also seems likely that this bug reappears there. It is perhaps useful to check this when fixing the bug in Alexander- The Cuff of the Son (Savage).
EDIT: I acquire the 74% chance based on 5 people taking the water damage, and thus a 1 in 5 chance of the initial target getting the next Compressed Water buff wiping this raid. Thus, there is an 80% chance of not encountering the bug. However, this mechanic occurs at least 6 times in the fight, and 0.8^6 = 0.262 = 26.2% chance of not encountering the bug in a successful run. Therefore, there is a 73.8% ~= 74% chance of encountering the bug and wiping unnecessarily.
EDIT: Written more clearly because videos exist out there with which players can find the information I wouldn't want to share otherwise, for progression purposes.