This has happened on an Intel and an AMD CPU system, it has happened on a 32GB memory Windows 10 pro system, to a 128GB memory Windows 11 Pro system, it has happened with Nvidia GPUs (RTX3060 12GB, RTX5090 32GB) and with AMD GPUs (RX580 8GB, RX7900XTX 24GB). So there is no "Aha, it's this GPU using this particular way of drawing this xyz that is the culprit."
Observations here include:
Multi Client
Client 1 to 6
Client 2 out of the 6 can be the one that experiences the issue, whilst the rest do not. Restarting the DDO Client will clear it for this client 2. Logging out and back in without restarting the client entirely (by logging out to the Desktop before logging back in) will leave this exactyl in place.
Theorised Stencil Shadows being associated with the issue is unsurprising, given observations I made saw that the triangles showed a scatter pattern from point sources and was roughly from where light sources are located in the map of the quest. Suggesting that it is something there that is used to draw those light sources that is not being loaded in with the rest of the quest assets and drawn that way instead. Or was unable to be loaded, resulting in what we see here.
The easiest way to replicate is to simply enter, see if there is a problem. Turn around, get back out. Reset quest and go in again. It was observed that this has happened in the middle of farming runs. So it didn't happen in the first run, didn't happen in the second, run, but it could happen at any point too, so first, second, third run, etc of the quest and it could happen to one of the clients.
J1NG