This is likely because bridge tiles exist on plane 1 no matter where they end up being rendered, and so get culled when Low Detail is telling the renderer to hide planes below the player's. Not too many places are affected by this I don't think, but a notable place is the bridge to Kril in the God Wars Dungeon, which is on plane 2 due to Saradomin's Encampment existing below the others and taking up planes 1 and 0.

Mentioned by Bruun in the Discord