I have now spoken with two FFXIV Customer Support Reps.

The boilerplate, not-entirely-Mac-grounded suggestions of the first I mention above.

The second response also seems to be somewhat generic/standardized, and mostly addresses connection problems, not anything like the above.

Here are the suggestions that were made initially. Note that they are claiming the system or another application is interfering with the game data, when logs very clearly indicate failures in FFXIV impacting the system, not the other way around. Also, they imply that FFXIV players should have NO other apps open when running the game regardless of specs, not even a single Chrome window (for example).

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The issue you are describing is most associated with interference with the game data. Most of the time, it results from certain security/privacy changes on Safari. Other times it occurs when an application that is running in the background is causing interference, such as Anti-virus software, firewalls, media players, web browsers, etc.

Please make sure all background applications (including anti-virus programs such as Norton, Kaspersky, etc.) have been disabled and/or closed to minimize game interference.

Ensure that the latest version of Safari is installed on your Mac (even if you don't use Safari). Once Safari is up-to-date, please open the Safari browser and make sure that all Browser History and Cookies/Web Data have been deleted. Please also make sure that "Cookies" are accepted and not being filtered.

Once these options have been adjusted, please run the Apple Update program to check that all firmware is up-to-date on your Mac OS. Once this process is complete, please re-launch the FINAL FANTASY XIV application.

If the suggestions provided above do not resolve the issue, then there is a communication error.
Check the following Port Ranges on your router/modem to ensure that the following Port Ranges have been opened/forwarded/triggered:
▼TCP
54992 through 54994,
55006 through 55007,
55021 through 55040

*You may learn how to do this by visiting http://www.portforward.com/
Find your specific router's brand and model number from the 'List of Routers' and you will be provided a step-by-step guide on how to access these port settings.
Otherwise, your ISP may forward these ports for you.*

If you have properly configured your router, and you are still experiencing these issues, our next suggestion is to bypass the router, and connect your computer directly to your modem. Please ensure that you power down both the modem and the computer for at least five minutes before attempting to connect to FINAL FANTASY XIV.

If you continue to receive these same errors when you are connected directly to the modem, then the problem lies with your ISP. We would recommend contacting your provider and advising them that one or more of the ports previously provided to you are being blocked or filtered, and that you do need access on these ports.