My friend recently remade our old vanilla server. We imported the old 1.9 world and he tried to optimize it before updating it to 1.13 but it failed. We got it to 1.13 anyways and sand that fell underwater would warp, jitter, and become invisible. We could both see it, and I recorded a video of it(sorry for the weird format I'm not good at video editing). I had been working above ground and sand was fine, and I couldn't replicate it in my single player copy of almost the same world. Since the major difference between my singleplayer world and the server world was the optimization I feel like that's part of the issue. We made a new 1.13 map and sand behaves normally. My singleplayer world had first been updated from 1.9 to 1.12 and then the snapshots and then 1.13.

Video demonstrating the issue: https://www.youtube.com/watch?v=RdsTP4y6VYw