Texture issues in packaged build


I currently have huge flickering textures all over the game world in a packaged build. In PIE or standalone game everything’s fine, but in a packaged build, it looks like in this video:

Previously, I thought it occurred on objects that were scaled up dramatically (for example some matte paintings used to be simple planes scaled 10k times or something) and fixed that by actually having meshes that size (and merge all matte paintings in a level). But now it appears again and I don’t think there are any objects scaled that big anymore. The textures that flicker are not the ones from the matte paintings anyway, so for some reason random textures appear somewhere in the world. The horizontal one in the video is at Z=0 and I didn’t find any actual meshes that were anywhere at that position and totally planar.

Do you have an idea what could cause this?