I received an ingame message from the Support Desk, asking me to submit video evidence (again through the Support Desk) to assist in researching the issue.

With the help of friends, FC mates and the wonderful folks of the Europeans on Aether community, I compiled a bunch of video material.
I figured I'd post it to the forums as well, but I can't respond to the bug report thread anymore now that it's been moved to the Accepted Bugs subforum.

So instead, I'm posting it here for future reference:

Quote Originally Posted by Nekkowe
Bug Report Escalation I.D.: https://forum.square-enix.com/ffxiv/threads/462053

Okay, here goes!

Responding to the Support Desk message I received on 2022-05-13, requesting assistance in researching this concern, here's some video footage of how the bug affects players on different latencies.

I would like to present, in order:

Exhibit A) https://www.youtube.com/watch?v=zUB64Q8KG_Y
This is video footage I recorded on a medium-to-high latency connection, displaying:
1. Starting at 0:00, a meandering and incomplete reintroduction of the issue.
2. At 4:56, the steps described in the thread: In the sequence of Cascade -> Fan Dance -> Fan Dance -> Fountain, the dual-weaved Fan Dance noticeably delays the next possible use of Fountain past the global recast cooldown (GCD).
3. At 7:29, an example for the Machinist job. It's impossible to smoothly single-weave Gauss Round or Ricochet between uses of Heat Blast while playing on medium-to-high latency. The next use of Heat Blast is always delayed by some time.

Exhibit B) https://www.youtube.com/watch?v=d8ANsW5Lxqs
This is video footage recorded by an acquaintance, Boo Mewrah.
It repeats the scenario of Exhibit A Step 2 on a lower latency connection. As you can see, dual-weaving Fan Dance after Cascade leaves plenty of time before the next possible use of Fountain. In this example, the next GCD action is not delayed whatsoever. Each action has the exact same cooldown as before, but a significantly shorter animation lock.

Exhibit C) https://www.youtube.com/watch?v=awEY9zNogrw
This is video footage recorded by an acquaintance, Kai Leonte, on the Chaos Data Center.
It displays a standard Machinist opener on a low latency connection (~25ms ping).
At 0:17, it repeats the scenario of Exhibit A Step 3.
Kai Leonte is able to perform what was impossible on my connection, smoothly single-weaving Gauss Round and Ricochet between uses of Heat Blast. Heat Blast can be reused on cooldown, without delay. Once again, each action has the exact same cooldown as before, but the character exits the animation lock much sooner after each of them.