Unusual graphics and texture errors on iMac Pro with Radeon Pro Vega 64

I recently purchased a new computer, an iMac Pro, and have noticed several major graphical errors in FFXIV that I did not have with my previous computer, a much older Mac Pro.

The most consistent error comes when rendering the textures of some character model skin (usually bare skin in certain cut scenes, but occasionally visible in the world at large), moving water in some lighting, and every instance of mist or fog beneath ground level (for instance, over the edge of the islands in the Churning Mists). In this error, the textures seem to be replaced by a grid with the actual texture shrunk to a tiny point in the middle of each box. Geometric lines on the model (which I presume to be the edges of rendering polygons) are unaffected, along with a little area around each. It's hard to describe, but I've been taking screenshots if that will help. The character texture effect is consistent for a given cut scene regardless of my computer's state at the time (i.e. freshly rebooted or on for a while, many programs open or no other programs open, etc.)

Also, I will sometimes get other graphical errors upon entering a new zone. Sometimes, this results in the HUD flickering a few times, and then vanishing entirely. Other times, it will cause lighting effects to be displayed as huge flat-color polygons radiating out from the light source. If it occurs when zoning in to a dungeon where I haven't yet watched the intro cinematic, it will briefly show the players at the start of the dungeon, then flicker in to the cinematic, and when it returns to the world both the lighting effect and the missing HUD will be in effect. In all these cases, if I tab out of the game at that point, it crashes.

I've tried adjusting my graphical settings several times, and have not yet found a combination that addresses any of these issues, though I probably haven't tried everything yet.

My specs:
iMac Pro (2017)
macOS Mojave (10.14.5)
Processor: 3 GHz Intel Xeon W
Memory: 64 GB 2666MHZ DDR4
Graphics: Radeon Pro Vega 64 16 GB
Display: Built-in Retina Display, 27-inch (5120 x 2880)

Good afternoon and thank you for posting on the Final Fantasy XIV Technical Support Forums.

What you are describing is an issue that has been reported before. The Square Enix Online Store page mentions issues with Radeon Pro Vega graphics cards. This is likely the issue you are running into.

I can provide some troubleshooting, however, it sounds like your issue is similar to the one already reported:

1) Try adjusting the resolution and graphical settings and see how this affects the glitches.

2) Make sure you Mac is fully updated.

3) Try a clean boot. Restart your Mac, then immediately press and hold the Shift key. The Apple logo will then appear on your display. Release the Shift key when you see the login window.

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!

Thanks for the quick response. In response to the troubleshooting:

1) I just went into the game and attempted adjusting all the graphical settings while observing the fog texture glitch (the easiest and most consistent one to observe). At every graphical resolution, from the lowest to the highest, the problem remained the same. I also switched between the preset graphics settings offered, and then went and manually lowered all the settings to their lowest degree, to similar lack of effect.

2) Just checked, and there is no software update available.

3) A clean boot also failed to change any of the problems.

It's possible that this is related to the problem listed on the store page, but the symptoms are different: the store page says that action icons may disappear, but that has never happened to me (except as part of the entire HUD disappearing). And the store page doesn't mention anything about glitched character model or fog textures.

It's possible that this is a problem I'll just have to resign myself to, but I wanted to at least try to see if there were any other options -- and possibly to get word passed along to the Mac development team, if it's a bug they might need to address.