The entire UI except portrait with buttons, compass, and strangely, the chatbox without the line to type on vanishes when zoomed out depending on the camera angle. I have to zoom in way too far to make sure I can see the UI. No menu I try to open is visible. (They apparently can still be used, as I zoomed in after clicking randomly trying to figure out what was wrong and I was deep into advanced options.)

I can always zoom in, it's just really annoying and I was wondering if anyone knew what the cause could be?

Edit: Apparently it's UI Lighting. With that disabled everything is always visible. Of course several button are blacked out, but the tooltip pops up when I hover the mouse over them, so I can at least read what the button is... Can't have everything I suppose.

Leaving this here incase anyone else runs into the problem or finds a better solution.

Game Options: Graphics - Tweaks - Advanced - Graphics Experimental Disable GUI Lighting

Uncheck that box to fix the vanishing issue.

Edit 2: WARNING Unchecking that box blacks out ALL MAIN MENU BUTTONS. Beamdog is full of morons, and apparently have never heard of beta testing. Now for the fun of trying to find that fucking option to fix it without being able to see any of the fucking menus... If anyone knows a proper method of fixing this shit, please let me know.

Ok, I still haven't found a solution, and it makes the game unplayable. This is ridiculous. I have to spin and zoom the camera wildly to find a spot the the UI appears just to bring up the tooltips. I've been through every option that looks like it could possibly affect this without any luck.

I don't understand why the UI would be affected by the camera angle. I turned off the bullethole thing, because I thought it was that, but it doesn't matter if there are 2nd floor graphics between me and the camera. The UI still flickers. Has no one else had this problem?

I have never had this issue, either with the original version or the more recent extended edition. The only thing that I have seen that is even remotely similar is years ago, I had a computer where I was missing some of the textures... but that was a compatibility issue with the graphics card in the computer that I had then.

Since it seems to be affecting entirely the user interface, maybe try using the Reborn UI as an override to see if that changes anything. The only thing that I can say about this is that not every module is 100% compatible with Reborn UI. I ran into some issues with some script events not triggering in Crimson Tides of Tethyr Enhanced Edition for example.
https://neverwintervault.org/project/nwnee/other/gui/reborn-ui