Some 2D UI elements missing occasionally, likely root cause inside

TL;DR for the render person - the 5 MiB vertex buffer used for Draw2D UI elements is too small.

As I've done render optimization work for Path of Building recently I was jokingly tagged in a discussion where someone experienced UI glitches in the game.

Problem:
In some situations a number of UI elements like the inventory grid, equipped gear, the skill bar, and the experience bar notches do not show up.

This is sensitive to having UI panels open on top of the passive skill tree and to the position/zoom and number of nodes allocated. By panning around the amount of missing UI elements can be altered.

This seems to be API agnostic, it happens on all three desktop APIs.

Video demonstration: https://i.imgur.com/q9B903n.mp4

Reproduction steps:
* Open the game in a wide resolution - this is needed to maximize the amount of nodes visible.
* Open the passive skill tree.
* Open the Inventory and Character panels.
* Zoom out as far as possible and try to get as many nodes and connectors in view at once.
* Observe flickering UI as you move around.

Effect:
When the problem manifests some UI elements will stop rendering based on the scene contents.
The first ones to go are currently the XP bar notches, followed by the mana globe, skill icons, menu button, inventory items and grid, equipped items and their sockets/gems/links, etc.

Cause:
When drawing the UI all Draw2D geometry seems to be sub-allocated from a single five megabyte vertex buffer. For pathological cases like the above this buffer can become full and no additional draw calls are made in the pass, losing some UI.

This can be observed from the outside via RenderDoc captures, where the buffer at the ultimate draw call is almost full, leaving no room for additional batches of geometry.

Good frame:
Bad frame:
Bad buffer:
Buffer creation:

bumping with maybe additional info, as I do not have a wide resolution / was just chillin in Karui.

https://clips.twitch.tv/DifficultTrappedWaspPicoMause-rKrFMlb7tXNB9-XT
https://imgur.com/a/LU8zkJk
report #592,095,252

Nice to see someone with a clue notice this issue, you can easily reproduce it by going to a Rogue Harbour and opening the passive tree and zooming right out on the tree.

UI elements will flicker and dissapear, even on a 4090 with 24gig of vid mem.

I believe this bug has been addressed in 3.23.0c.

There's a patch note of "Fixed a rare bug where parts of the UI could briefly disappear." and since that patch the buffer has been buffed by 40% to 7 MiB.

UI still glitching and partially disappears while in a 6 ppl party with 100+ minions 500+ projectiles on the screen.