I’m having the same issue on my survival multiplayer realm. When in download the world from my realm and load it in singleplayer the issues are gone but when i re-upload the world the same issues appear again. I get lines of light all over my world. Mostly in chunks i loaded previously. New chunks look like they’re fine. The light lines generate right on, or next to every other chunkborder in the world.
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It doesn’t appear to be present when you view it from the mobile version of the game.