Hello,
Having used the free camera to review the situation, it seems the issue is at certain distances the LOD *beneath* the stairs vanishes, allowing things to shine through.
But when you pull close to it, the issue vanishes utterly as the items below the stairs load.
https://imgur.com/a/bLH9kZ3
The objects that are vanishing are: NorTmpExtPlatCorOut01Snow, Base ID of 00026FD2, last changed by stretched snow begone. LOD is Lod\NordicExterior\NorTmpExtPlatCorOut01_LOD.nif. Stretched Snow Begone would not effect the distance at which an object vansihes, I believe.
See below for log.
https://zerobin.net/?bc92868796143cf5#OSwU0g4wYarNpYAm6YRiHvABL3wO16OfLSFx5UQxB9k=