MCPE Bug/Glitch 1.16.40

When me and my cousin join using lan multiplayer I lagged so much when I fly into a random coords using a elytra I saw a grass blocks turn into snow grass blocks and theres a glitch or bug happening on top of them theres like purple and black thingy on top of them, but when I unload the chunk and came back the bug or glitch was gone

Note: I put down 1.16.210 bec theres no 1.16.40 (this bug or glitch happened on mcpe 1.16.40 lan multiplayer)