Changes to Turn 2
All boss encounters in FFXIV use what we internally refer to as a monitoring program and gambit algorithms to dictate their behavior.
The monitoring program takes the following factors into account for every encounter:
The number of participating players
The HP and enmity level of all participating players
The HP of the boss enemy
The boss enemy's target
Time elapsed since the beginning of the encounter
By monitoring these factors, bosses are able to transition from one phase to the next, and activate certain abilities such as Titan's Upheaval or the fully charged ADS in Turn 2 of the Binding Coil.
However there was a latent bug (albeit a rarely occurring one) that can potentially cause conditions of the instance to reset based on the monitored player count, causing the boss to disappear and respawn.
This bug fix was implemented under the assumption that it would have no effect on Turn 2 when completed in the manner it was designed. However, the popular strategy used to bypass Allagan Rot involves players attacking the ADS after the program has completed monitoring boss behavior. As a result, attack frequency as determined by player count has changed from its pre-2.16 functionality.
Although the development team has no problem with the strategy used to bypass Allagan Rot, this bug fix inadvertently affected players' ability to employ said strategy.
Because the reason for this bug fix was to address an issue with a very miniscule chance of being triggered, we will revert the monitoring program back to its 2.15 functionality, and have our QA team confirm this revision.
Changes to Turn 5
The changes seen in Turn 5 are the result of changes intended for patch 2.2 being implemented in patch 2.16.
An adjustment to enemy target evaluation was made to prevent bugs in encounters for patch 2.2, but this change was also applied to the 2.16 patch, causing Twintania to exhibit unusual behavior.
Prior to patch 2.16, this encounter was designed so that players targeted by Conflagration could not be targeted, but with this change, Twintania will now switch targets if it is determined that the current target cannot be attacked. Because Conflagration does not target the top two players on the enmity list, an often-used strategy is for the player with aggro to enter the Conflagration, thereby negating Twintania's attacks. However, this change in Twintania's behavior has made this tactic more risky to employ.
Because this change would drastically affect established tactics, as well as the difficulty of Turn 5, we will be reverting these changes alongside the revisions being made to Turn 2. Addressing these issues is currently our top priority, and as soon as we have confirmed that the fixes are functioning properly, we will create a patch and take down all Worlds for an emergency maintenance.
I cannot express how sorry I am for the trouble this oversight by our team has caused. An announcement will be made as soon as we've confirmed the time of emergency maintenance, but in the meantime, I ask for your patience as we work to address these issues in a thorough, timely manner.