Sky is incorrectly rendered through cave walls at certain viewing distances

While exploring a large underground cave, parts of the cave sometimes fail to render correctly when viewed from a certain distance. The missing area instead shows the outdoor sky, even though I am deep underground. The sky also appears to match the current time of day (blue sky during daytime and dark sky at night).

Steps to reproduce:

1. Enter the large cave shown in the attached screenshots.

2. Look toward the affected area from a distance.

3. At certain positions, the cave terrain disappears and the outdoor sky becomes visible through it.

4. Move toward the affected area. There appears to be a distinct boundary where the terrain suddenly renders normally again.

I have observed this several times at the same location. Usually the terrain returns to normal as I approach it, but on one occasion the incorrect rendering remained even after I reached the affected area.

Expected result:
The cave walls and terrain should render normally and completely block the view of the outdoor sky.

Actual result:
Parts of the cave terrain are not rendered, allowing the outdoor sky to be seen from underground.